General Approach to Anemias
Anemia is present in adults if the hematocrit is below 41% (hemoglobin less than 13.5 g/dL [135 g/L]) in males or below 36% (hemoglobin less than 12 g/dL [120 g/L]) in females. Congenital anemia is suggested by the patient’s personal and family history. The most common cause of anemia is iron deficiency. Poor diet may result in folic acid deficiency and contribute to iron deficiency, but bleeding is the most common cause of iron deficiency in adults. Physical examination demonstrates pallor. Attention to physical signs of primary hematologic diseases (lymphadenopathy; hepatosplenomegaly; or bone tenderness, especially in the sternum or anterior tibia) is important. Mucosal changes such as a smooth tongue suggest megaloblastic anemia.
Anemias are classified according to their pathophysiologic basis, ie, whether related to diminished production (relative or absolute reticulocytopenia) or to increased production due to accelerated loss of red blood cells (reticulocytosis) (Table 13–1), and according to red blood cell size (Table 13–2). A reticulocytosis occurs in one of three pathophysiologic states: acute blood loss, recent replacement of a missing erythropoietic nutrient, or reduced red blood cell survival (ie, hemolysis). A severely microcytic anemia (mean corpuscular volume [MCV] less than 70 fL) is due either to iron deficiency or thalassemia, while a severely macrocytic anemia (MCV greater than 120 fL) is almost always due to either megaloblastic anemia or to cold agglutinins in blood analyzed at room temperature. A bone marrow biopsy is generally needed to complete the evaluation of anemia when the laboratory evaluation fails to reveal an etiology, when there are additional cytopenias present, or when an underlying primary or secondary bone marrow process is suspected.
Table 13–1.Classification of anemia by pathophysiology. |Favorite Table|Download (.pdf) Table 13–1. Classification of anemia by pathophysiology.
Decreased red blood cell production (relative or absolute reticulocytopenia)
Hemoglobin synthesis lesion: iron deficiency, thalassemia, anemia of chronic disease, hypoerythropoietinemia
DNA synthesis lesion: megaloblastic anemia, DNA synthesis inhibitor medications
Hematopoietic stem cell lesion: aplastic anemia, leukemia
Bone marrow infiltration: carcinoma, lymphoma, fibrosis, sarcoidosis, Gaucher disease, others
Immune-mediated inhibition: aplastic anemia, pure red cell aplasia
Increased red blood cell destruction or accelerated red blood cell loss (reticulocytosis)
Acute blood loss
Membrane lesion: hereditary spherocytosis, elliptocytosis
Hemoglobin lesion: sickle cell, unstable hemoglobin
Glycolysis abnormality: pyruvate kinase deficiency
Oxidation lesion: glucose-6-phosphate dehydrogenase deficiency
Immune: warm antibody, cold antibody
Microangiopathic: thrombotic thrombocytopenic purpura, hemolytic-uremic syndrome, mechanical cardiac valve, paravalvular leak
Infection: Clostridium perfringens, malaria
Table 13–2.Classification of anemia by mean red blood cell volume (MCV). |Favorite Table|Download (.pdf) Table 13–2. Classification of anemia by mean red blood cell volume (MCV).
Anemia of chronic disease
Vitamin B12 deficiency
DNA synthesis inhibitors
Bone marrow failure state (eg, aplastic anemia, marrow infiltrative disorder, etc)
Non-thyroid endocrine gland failure
Mild form of most acquired microcytic or macrocytic etiologies of anemia
ESSENTIALS OF DIAGNOSIS
Iron deficiency is present if serum ferritin is less than 12 ng/mL (27 pmol/L) or less than 30 ng/mL (67 pmol/L) if also anemic.
Caused by bleeding unless proved otherwise.
Responds to iron therapy.
Iron deficiency is the most common cause of anemia worldwide. The causes are listed in Table 13–3. Aside from circulating red blood cells, the major location of iron in the body is the storage pool as ferritin or as hemosiderin in macrophages.
Table 13–3.Causes of iron deficiency. |Favorite Table|Download (.pdf) Table 13–3. Causes of iron deficiency.
Helicobacter pylori gastritis
Hereditary iron-refractory iron deficiency anemia
Blood loss (chronic)
The average American diet contains 10–15 mg of iron per day. About 10% of this amount is absorbed in the stomach, duodenum, and upper jejunum under acidic conditions. Dietary iron present as heme is efficiently absorbed (10–20%) but nonheme iron less so (1–5%), largely because of interference by phosphates, tannins, and other food constituents. The major iron transporter from the diet across the intestinal lumen is ferroportin, which also facilitates the transport of iron to apotransferrin in macrophages for delivery to erythroid cells prepared to synthesize hemoglobin. Hepcidin, which is increasingly produced during inflammation, negatively regulates iron transport by promoting the degradation of ferroportin. Small amounts of iron—approximately 1 mg/day—are normally lost through exfoliation of skin and mucosal cells.
With hemorrhage, there is decreased oxygen delivery to the kidneys resulting in stabilization of a hypoxia-inducible factor in the kidneys and increased erythropoietin generation in the kidneys and liver. Erythropoietin stimulates erythropoiesis, leading to an increased synthesis of erythroferrone. In turn, erythroferrone suppresses hepcidin synthesis leading to ferroportin stability and enhanced iron transport across the gastrointestinal lumen.
Menstrual blood loss plays a major role in iron metabolism. The average monthly menstrual blood loss is approximately 50 mL but may be five times greater in some individuals. Women with heavy menstrual losses must absorb 3–4 mg of iron from the diet each day to maintain adequate iron stores, which is not commonly achieved. Women with menorrhagia of this degree will almost always become iron deficient without iron supplementation.
In general, iron metabolism is balanced between absorption of 1 mg/day and loss of 1 mg/day. Pregnancy and lactation upset the iron balance, since requirements increase to 2–5 mg of iron per day. Normal dietary iron cannot supply these requirements, and medicinal iron is needed during pregnancy and lactation. Decreased iron absorption can also cause iron deficiency, such as in people affected by celiac disease, and it also commonly occurs after gastric resection or jejunal bypass surgery.
The most important cause of iron deficiency anemia in adults is chronic blood loss, especially menstrual and gastrointestinal blood loss. Iron deficiency demands a search for a source of gastrointestinal bleeding if other sites of blood loss (menorrhagia, other uterine bleeding, and repeated blood donations) are excluded. Prolonged aspirin or nonsteroidal anti-inflammatory drug use may cause it even without a documented structural lesion. Celiac disease (gluten enteropathy), even when asymptomatic, can cause iron deficiency through poor absorption in the gastrointestinal tract. Zinc deficiency is another cause of poor iron absorption. Chronic hemoglobinuria may lead to iron deficiency, but this is uncommon. Traumatic hemolysis due to a prosthetic cardiac valve and other causes of intravascular hemolysis (eg, paroxysmal nocturnal hemoglobinuria) should also be considered. The cause of iron deficiency is not found in up to 5% of cases.
Pure iron deficiency might prove refractory to oral iron replacement. Refractoriness is defined as a hemoglobin increment of less than 1 g/dL (10 g/L) after 4–6 weeks of 100 mg/day of elemental oral iron. The differential diagnosis in these cases (Table 13–3) includes malabsorption from autoimmune gastritis, Helicobacter pylori gastric infection, celiac disease, and hereditary iron-refractory iron deficiency anemia. Iron-refractory iron deficiency anemia is a rare autosomal recessive disorder due to mutations in the transmembrane serine protease 6 (TMPRSS6) gene, which normally down-regulates hepcidin. In iron-refractory iron deficiency anemia, hepcidin levels are normal to high and ferritin levels are high despite the iron deficiency.
The primary symptoms of iron deficiency anemia are those of the anemia itself (easy fatigability, tachycardia, palpitations, and dyspnea on exertion). Severe deficiency causes skin and mucosal changes, including a smooth tongue, brittle nails, spooning of nails (koilonychia), and cheilosis. Dysphagia due to the formation of esophageal webs (Plummer-Vinson syndrome) may occur in severe iron deficiency. Many iron-deficient patients develop pica, craving for specific foods (ice chips, etc) often not rich in iron.
Iron deficiency develops in stages. The first is depletion of iron stores without anemia followed by anemia with a normal red blood cell size (normal MCV) followed by anemia with reduced red blood cell size (low MCV). The reticulocyte count is low or inappropriately normal. Ferritin is a measure of total body iron stores. A ferritin value less than 12 ng/mL (27 pmol/L) (in the absence of scurvy) is a highly reliable indicator of reduced iron stores. Note that the lower limit of normal for ferritin generally is below 12 ng/mL (27 pmol/L) in women due to the fact that the normal ferritin range is generated by including healthy menstruating women who are iron deficient but not anemic. However, because serum ferritin levels may rise in response to inflammation or other stimuli, a normal or elevated ferritin level does not exclude a diagnosis of iron deficiency. A ferritin level less than 30 ng/mL (67 pmol/L) almost always indicates iron deficiency in anyone who is anemic. As iron deficiency progresses, serum iron values decline to less than 30 mcg/dL (67 pmol/L) and transferrin (the iron transport protein) levels rise to compensate, leading to transferrin saturations of less than 15%. Low transferrin saturation is also seen in anemia of inflammation, so caution in the interpretation of this test is warranted. Isolated iron deficiency anemia has a low hepcidin level, not yet a clinically available test. As the MCV falls (ie, microcytosis), the blood smear shows hypochromic microcytic cells (eFigure 13–1). With further progression, anisocytosis (variations in red blood cell size) and poikilocytosis (variation in shape of red cells) develop. Severe iron deficiency will produce a bizarre peripheral blood smear, with severely hypochromic cells, target cells, and pencil-shaped or cigar-shaped cells. Bone marrow biopsy for evaluation of iron stores is rarely performed. If the biopsy is done, it shows the absence of iron in erythroid progenitor cells by Prussian blue staining. The platelet count is commonly increased, but it usually remains under 800,000/mcL (800 × 109/L).
Iron deficiency anemia. (Peripheral blood, 50 ×.) Hypochromic and microcytic cells due to iron deficiency. The diameter of the normal red blood cell should be approximately the same as that of the nucleus of a small lymphocyte. This smear shows that most of the red cells are much smaller than the lymphocytes. This patient also has an increased platelet count—a common finding in patients with iron deficiency. (Used, with permission, from L Damon.)
Other causes of microcytic anemia include anemia of chronic disease (specifically, anemia of inflammation), thalassemia, lead poisoning, and congenital X-linked sideroblastic anemia. Anemia of chronic disease is characterized by normal or increased iron stores in bone marrow macrophages and a normal or elevated ferritin level; the serum iron and transferrin saturation are low, often drastically so, and the total iron-binding capacity (TIBC) (the blood’s capacity for iron to bind to transferrin) and transferrin are either normal or low. Thalassemia produces a greater degree of microcytosis for any given level of anemia than does iron deficiency and, unlike virtually every other cause of anemia, has a normal or elevated (rather than a low) red blood cell count as well as a reticulocytosis. In thalassemia, red blood cell morphology on the peripheral smear resembles severe iron deficiency.
The diagnosis of iron deficiency anemia can be made either by the laboratory demonstration of an iron-deficient state or by evaluating the response to a therapeutic trial of iron replacement. Since the anemia itself is rarely life-threatening, the most important part of management is identification of the cause—especially a source of occult blood loss.
Ferrous sulfate, 325 mg once daily on an empty stomach, is a standard approach for replenishing iron stores. As oral iron stimulates hepcidin production, once daily dosing maximizes iron absorption compared to multiple daily dosing, and with fewer side effects. Nausea and constipation limit compliance with ferrous sulfate. Extended-release ferrous sulfate with mucoprotease is a well tolerated oral preparation. Taking ferrous sulfate with food reduces side effects but also its absorption. An appropriate response is a return of the hematocrit level halfway toward normal within 3 weeks with full return to baseline after 2 months. Iron therapy should continue for 3–6 months after restoration of normal hematologic values to replenish iron stores. Failure of response to iron therapy is usually due to noncompliance, although occasional patients may absorb iron poorly, particularly if the stomach is achlorhydric. Such patients may benefit from concomitant administration of oral ascorbic acid. Other reasons for failure to respond include incorrect diagnosis (anemia of chronic disease, thalassemia), celiac disease, and ongoing gastrointestinal blood loss that exceeds the rate of new erythropoiesis. Treatment of H pylori infection, in appropriate cases, can improve oral iron absorption.
The indications are intolerance of or refractoriness to oral iron (including those with iron-refractory iron deficiency anemia), gastrointestinal disease (usually inflammatory bowel disease) precluding the use of oral iron, and continued blood loss that cannot be corrected, such as chronic hemodialysis. Parenteral iron preparations coat the iron in protective carbohydrate shells. Historical parenteral iron preparations, such as iron dextran, were problematic due to long infusion times (hours), polyarthralgia, and hypersensitivity reactions, including anaphylaxis. Current preparations are safe and can be infused in less than 5 minutes. Iron oxide coated with polyglucose sorbitol carboxymethyl-ether can be given in doses up to 510 mg by intravenous bolus over 15 minutes, with no test dose required. Most iron deficient patients need 1–1.5 g of parenteral iron; this dose corrects for the iron deficit and replenishes iron stores for the future.
The iron deficit is calculated by determining the decrement in red cell volume from normal, recognizing there is 1 mg of iron in each milliliter of red blood cells. Total body iron ranges between 2 g and 4 g: approximately 50 mg/kg in men and 35 mg/kg in women. Most (70–95%) of the iron is present in hemoglobin in circulating red blood cells. In men, red blood cell volume is approximately 30 mL/kg; in women, it is about 27 mL/kg. Thus, a 50-kg woman whose hemoglobin is 9 g/dL (75% of normal) has an iron deficit of 0.25 × 27 mL/kg × 50 kg = 337.5 mL of red blood cells (or 337.5 mg of iron). The parenteral iron dose is the iron deficit plus (usually) 1 extra gram to replenish iron stores and anticipate further iron loses, so in this case 1.4 g.
Ferric pyrophosphate citrate (Triferic), approved by the FDA in 2015 to replace the 5–7 mg of iron CKD patients tend to lose to each hemodialysis, is added to the dialysate. It appears to be able to deliver sufficient iron to the marrow to maintain hemoglobin and not increase iron stores; it may obviate the need for intravenous iron in hemodialysis patients.
Patients should be referred to a hematologist if the suspected diagnosis is not confirmed or if they are not responsive to oral iron therapy.
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et al. Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women. Blood. 2015 Oct 22;126(17):1981–9.
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et al. Comparative risk of anaphylactic reactions associated with intravenous iron products. JAMA. 2015 Nov 17;314(19):2062–8.
ANEMIA OF CHRONIC DISEASE
ESSENTIALS OF DIAGNOSIS
Mild or moderate normocytic or microcytic anemia.
Normal or increased ferritin and normal or reduced transferrin.
Underlying chronic disease.
Many chronic systemic diseases are associated with mild or moderate anemia. The anemias of chronic disease are characterized according to etiology and pathophysiology. First, the anemia of inflammation is associated with chronic inflammatory states (such as inflammatory bowel disease, rheumatoid arthritis, chronic infections, and malignancy) and is mediated through hepcidin (a negative regulator of ferroportin), resulting in reduced iron uptake in the gut and reduced iron transfer from macrophages to erythroid progenitor cells in the bone marrow. This is referred to as iron-restricted erythropoiesis since the patient is iron replete. There is also reduced responsiveness to erythropoietin, the elaboration of hemolysins that shorten red blood cell survival, and the production of inflammatory cytokines that dampen red cell production. The serum iron is low in the anemia of inflammation. Second, the anemia of organ failure can occur with kidney disease, hepatic failure, and endocrine gland failure. Erythropoietin is reduced and the red blood cell mass decreases in response to the diminished signal for red blood cell production; the serum iron is normal (except in chronic kidney disease where it is low due to the reduced hepcidin clearance and subsequent enhanced degradation of ferroportin). Third, the anemia of older adults is present in up to 20% of individuals over age 85 years in whom a thorough evaluation for an explanation of anemia is negative. It is a consequence of a relative resistance to red blood cell production in response to erythropoietin, a decrease in erythropoietin production relative to the nephron mass, and a negative erythropoietic influence of low levels of chronic inflammatory cytokines in older adults; the serum iron is normal.
The clinical features are those of the causative condition. The diagnosis should be suspected in patients with known chronic diseases. In cases of significant anemia, coexistent iron deficiency or folic acid deficiency should be suspected. Decreased dietary intake of iron or folic acid is common in chronically ill patients, many of whom will also have ongoing gastrointestinal blood losses. Patients undergoing hemodialysis regularly lose both iron and folic acid during dialysis.
The hematocrit rarely falls below 60% of baseline (except in kidney failure). The MCV is usually normal or slightly reduced. Red blood cell morphology is usually normal, and the reticulocyte count is mildly decreased or normal. In the anemia of inflammation, serum iron and transferrin values are low, and the transferrin saturation may be extremely low, leading to an erroneous diagnosis of iron deficiency. In contrast to iron deficiency, serum ferritin values should be normal or increased. A serum ferritin value less than 30 ng/mL (67 pmol/L) indicates coexistent iron deficiency. Classic anemia of inflammation has elevated hepcidin levels; however, no clinical test is yet available. In the anemias of organ failure and of older adults, the iron studies are generally normal. The anemia of older persons is a diagnosis of exclusion in a patient with anemia who is over age 65 years.
A particular challenge is the diagnosis of iron deficiency in the setting of the anemia of inflammation in which the serum ferritin can be as high as 200 ng/mL (450 pmol/L). The diagnosis is established by a bone marrow biopsy with iron stain. Absent iron staining indicates iron deficiency, whereas iron localized in marrow macrophages indicates pure anemia of inflammation. However, bone marrow biopsies are rarely done for this purpose. Three other tests all support iron deficiency in the setting of inflammation: a reticulocyte hemoglobin concentration of less than 28 pg; a normal hepcidin level; or a soluble serum transferrin receptor (units: mg/L) to log ferritin (units: mcg/L) ratio of 1–8 (a ratio of less than 1 is virtually diagnostic of pure anemia of chronic disease). A functional test is hemoglobin response to oral or parenteral iron in the setting of inflammation when iron deficiency is suspected. A note of caution: certain circumstances of iron-restricted erythropoiesis (such as malignancy) will partially respond to parenteral iron infusion even when the iron stores are replete due to the immediate distribution of iron to erythropoietic progenitor cells after the infusion.
In most cases, no treatment of the anemia is necessary and the primary management is to address the condition causing the anemia of chronic disease. When the anemia is severe or is adversely affecting the quality of life or functional status, then treatment involves either red blood cell transfusions or parenteral recombinant erythropoietin (epoetin alfa or darbepoetin). The indications for recombinant erythropoietin are hemoglobin less than 10 g/dL and anemia due to rheumatoid arthritis, inflammatory bowel disease, hepatitis C, zidovudine therapy in HIV-infected patients, myelosuppressive chemotherapy of solid malignancy (treated with palliative intent only), or chronic kidney disease (estimated glomerular filtration rate of less than 60 mL/min). The dosing and schedule of recombinant erythropoietin are individualized to maintain the hemoglobin between 10 g/dL (100 g/L) and 12 g/dL (120 g/L). The use of recombinant erythropoietin is associated with an increased risk of venothromboembolism and arterial thrombotic episodes, especially if the hemoglobin rises to greater than 12 g/dL (120 g/L). There is concern that recombinant erythropoietin is associated with reduced survival in patients with malignancy. For patients with end-stage renal disease receiving recombinant erythropoietin who are on hemodialysis, the anemia of chronic kidney disease can be more effectively corrected by adding soluble ferric pyrophosphate to their dialysate than by administering intravenous iron supplementation.
Referral to a hematologist is not usually necessary.
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et al. Anemia of chronic disease: a unique defect of iron recycling for many different chronic diseases. Eur J Intern Med. 2014 Jan;25(1):12–7.
ESSENTIALS OF DIAGNOSIS
Microcytosis disproportionate to the degree of anemia.
Positive family history.
Lifelong personal history of microcytic anemia.
Normal or elevated red blood cell count.
Abnormal red blood cell morphology with microcytes, hypochromia, acanthocytes, and target cells.
In beta-thalassemia, elevated levels of hemoglobin A2 or F.
The thalassemias are hereditary disorders characterized by reduction in the synthesis of globin chains (alpha or beta). Reduced globin chain synthesis causes reduced hemoglobin synthesis and a hypochromic microcytic anemia because of defective hemoglobinization of red blood cells. Thalassemias can be considered among the hyperproliferative hemolytic anemias, the anemias related to abnormal hemoglobin, and the hypoproliferative anemias, since all of these factors play a role in pathogenesis. The hallmark laboratory features are small (low MCV) and pale (low mean corpuscular hemoglobin [MCH]) red blood cells, anemia, and a normal to elevated red blood cell count (ie, a large number of the small and pale red blood cells are being produced). Although patients often exhibit an elevated reticulocyte count, generally the degree of reticulocyte output is inadequate to meet the degree of red blood cell destruction (hemolysis) occurring in the bone marrow and the patients remain anemic.
Normal adult hemoglobin is primarily hemoglobin A, which represents approximately 98% of circulating hemoglobin. Hemoglobin A is formed from a tetramer of two alpha chains and two beta globin chains—and is designated alpha2beta2. Two copies of the alpha-globin gene are located on each chromosome 16, and there is no substitute for alpha-globin in the formation of adult hemoglobin. One copy of the beta-globin gene resides on each chromosome 11 adjacent to genes encoding the beta-like globins delta and gamma (the so-called beta-globin gene cluster region). The tetramer of alpha2delta2 forms hemoglobin A2, which normally comprises 1–3% of adult hemoglobin. The tetramer alpha2gamma2 forms hemoglobin F, which is the major hemoglobin of fetal life but which comprises less than 1% of normal adult hemoglobin.
The thalassemias are described as “trait” when there are laboratory features without significant clinical impact, “intermedia” when there is an occasional red blood cell transfusion requirement or other moderate clinical impact, and “major” when the disorder is life-threatening and the patient is transfusion-dependent. Most patients with thalassemia major die of the consequences of iron overload from RBC transfusions.
Alpha-thalassemia is due primarily to gene deletions causing reduced alpha-globin chain synthesis (Table 13–4). Each alpha-globin gene produces one-quarter of the total alpha-globin quantity, so there is a predictable proportionate decrease in alpha-globin output with each lost alpha-globin gene. Since all adult hemoglobins are alpha containing, alpha-thalassemia produces no change in the proportions of hemoglobins A, A2, and F on hemoglobin electrophoresis. In severe forms of alpha-thalassemia, excess beta chains may form a beta-4 tetramer called hemoglobin H. In the presence of reduced alpha chains, the excess beta chains are unstable and precipitate, leading to damage of red blood cell membranes. This leads to both intramedullary (bone marrow) and peripheral blood hemolysis.
Table 13–4.Alpha-thalassemia syndromes. |Favorite Table|Download (.pdf) Table 13–4. Alpha-thalassemia syndromes.
|Number of Alpha-Globin Genes Transcribed ||Syndrome ||Hematocrit ||MCV |
|4 ||Normal ||Normal ||Normal |
|3 ||Silent carrier ||Normal ||Normal |
|2 ||Thalassemia minor (or trait) ||28–40% ||60–75 fL |
|1 ||Hemoglobin H disease ||22–32% ||60–70 fL |
|0 ||Hydrops fetalis1 ||< 18% ||< 60 fL |
Beta-thalassemias are usually caused by point mutations rather than deletions (Table 13–5). These mutations result in premature chain termination or in problems with transcription of RNA and ultimately result in reduced or absent beta-globin chain synthesis. The molecular defects leading to beta-thalassemia are numerous and heterogeneous. Defects that result in absent beta-globin chain expression are termed beta0, whereas those causing reduced but not absent synthesis are termed beta+. In beta+ thalassemia, the degree of reduction of beta-globin synthesis is consistent within families but is quite variable between families. The reduced beta-globin chain synthesis in beta-thalassemia results in a relative increase in the proportions of hemoglobins A2 and F compared to hemoglobin A on hemoglobin electrophoresis, as the beta-like globins (delta and gamma) substitute for the missing beta chains. In the presence of reduced beta chains, the excess alpha chains are unstable and precipitate, leading to damage of red blood cell membranes. This leads to both intramedullary (bone marrow) and peripheral blood hemolysis. The bone marrow demonstrates erythroid hyperplasia under the stimuli of anemia and ineffective erythropoiesis (intramedullary destruction of the developing erythroid cells). In cases of severe thalassemia, the marked expansion of the erythroid compartment in the bone marrow may cause severe bony deformities, osteopenia, and pathologic bone fractures.
Table 13–5.Beta-thalassemia syndromes. |Favorite Table|Download (.pdf) Table 13–5. Beta-thalassemia syndromes.
| ||Beta-Globin Genes Transcribed ||Hb A ||Hb A2 ||Hb F ||Transfusions |
|Normal ||Homozygous beta ||97–99% ||1–3% ||< 1% || |
|Thalassemia minor ||Heterozygous beta0 ||80–95% ||4–8% ||1–5% ||None |
| ||Heterozygous beta+ ||80–95% ||4–8% ||1–5% ||None |
|Thalassemia intermedia ||Homozygous beta+ (mild) ||0–30% ||0–10% ||6–100% ||Occasional |
|Thalassemia major ||Homozygous beta0 ||0% ||4–10% ||90–96% ||Dependent |
|Thalassemia major ||Homozygous beta+ ||0–10% ||4–10% ||90–96% ||Dependent |
The alpha-thalassemia syndromes are seen primarily in persons from southeast Asia and China, and, less commonly, in blacks and persons of Mediterranean origin (Table 13–4). Normally, adults have four copies of the alpha-globin chain. When three alpha-globin genes are present, the patient is hematologically normal (silent carrier). When two alpha-globin genes are present, the patient is said to have alpha-thalassemia trait, a form of thalassemia minor. In alpha-thalassemia-1 trait, the alpha gene deletion is heterozygous (alpha –/alpha –) and affects mainly those of Asian descent. In alpha-thalassemia-2 trait, the alpha gene deletion is homozygous (alpha alpha/– –) and affects mainly blacks. These patients are clinically normal and have a normal life expectancy and performance status, with a mild microcytic anemia. When only one alpha globin chain is present (alpha –/– –), the patient has hemoglobin H disease (alpha-thalassemia-3). This is a chronic hemolytic anemia of variable severity (thalassemia minor or intermedia). Physical examination might reveal pallor and splenomegaly. Affected individuals usually do not need transfusions; however, they may be required during transient periods of hemolytic exacerbation caused by infection or other stressors or during periods of erythropoietic shutdown caused by certain viruses (“aplastic crisis”). When all four alpha-globin genes are deleted, no normal hemoglobin is produced and the affected fetus is stillborn (hydrops fetalis). In hydrops fetalis, the only hemoglobin species gamma made is called hemoglobin Bart’s (gamma4).
Beta-thalassemia primarily affects persons of Mediterranean origin (Italian, Greek) and to a lesser extent Asians and blacks (Table 13–5). Patients homozygous for beta-thalassemia (beta0/beta0 or some with beta+/beta+) have thalassemia major (Cooley anemia). Affected children are normal at birth but after 6 months, when hemoglobin synthesis switches from hemoglobin F to hemoglobin A, severe anemia requiring transfusion develops. Numerous clinical problems ensue, including stunted growth, bony deformities (abnormal facial structure, pathologic bone fractures), hepatosplenomegaly, jaundice (due to gallstones, hepatitis-related cirrhosis, or both), and thrombophilia. The clinical course is modified significantly by transfusion therapy, but transfusional iron overload (hemosiderosis) results in a clinical picture similar to hemochromatosis, with heart failure, cardiac arrhythmias, cirrhosis, endocrinopathies, and pseudoxanthoma elasticum (calcification and fragmentation of the elastic fibers of the skin, retina, and cardiovascular system), usually after more than 100 units of red blood cells have been transfused. Iron overloading occurs because the human body has no active iron excretory mechanism. Before the application of allogeneic stem cell transplantation and the development of more effective forms of iron chelation, death from iron overload usually occurred between the ages of 20 and 30 years.
Patients homozygous for a milder form of beta-thalassemia (beta+/beta+, but allowing a higher rate of beta-globin synthesis) have thalassemia intermedia. These patients have chronic hemolytic anemia but do not require transfusions except under periods of stress or during aplastic crises. They also may develop iron overload because of periodic transfusion. They survive into adult life but with hepatosplenomegaly and bony deformities. Patients heterozygous for beta-thalassemia (beta/beta0 or beta/beta+) have thalassemia minor and a clinically insignificant microcytic anemia.
Prenatal diagnosis is available, and genetic counseling should be offered and the opportunity for prenatal diagnosis discussed.
1. Alpha-thalassemia trait
These patients have mild anemia, with hematocrits between 28% and 40%. The MCV is strikingly low (60–75 fL) despite the modest anemia, and the red blood count is normal or increased. The peripheral blood smear shows microcytes, hypochromia, occasional target cells, and acanthocytes (cells with irregularly spaced spiked projections) (eFigure 13–2). The reticulocyte count and iron parameters are normal. Hemoglobin electrophoresis is normal. Alpha-thalassemia trait is thus usually diagnosed by exclusion. Genetic testing to demonstrate alpha-globin gene deletion is available.
Alpha-Thalassemia trait. (Peripheral blood, 50 ×.) Mildly hypochromic and microcytic cells with occasional target cells in a patient with alpha-thalassemia trait (the absence of two alpha-globin genes). Note that the red blood cells are slightly smaller than the small lymphocyte nucleus shown in the center of the field. (Used, with permission, from L Damon.)
These patients have a more marked anemia, with hematocrits between 22% and 32%. The MCV is remarkably low (60–70 fL) and the peripheral blood smear is markedly abnormal, with hypochromia, microcytosis, target cells, and poikilocytosis. The reticulocyte count is elevated and the red blood cell count is normal or elevated. Hemoglobin electrophoresis will show a fast-migrating hemoglobin (hemoglobin H), which comprises 10–40% of the hemoglobin. A peripheral blood smear can be stained with supravital dyes to demonstrate the presence of hemoglobin H (eFigure 13–3).
Hemoglobin H disease. (Peripheral blood, 50 ×.) This smear from a patient with severe alpha-thalassemia shows hypochromic, microcytic cells, target cells, and bizarre shapes. These changes are the consequence of loss of three alpha-globin genes. The reticulocyte count is elevated since this is a hemolytic state due to the mispairing of beta-globin units in the marrow compartment. Hemoglobin H is the tetramer of four beta-globin units. Some red blood cells appear normal in this smear because this patient had recently received a blood transfusion. (Used, with permission, from L Damon.)
3. Beta-thalassemia minor
These patients have a modest anemia with hematocrit between 28% and 40%. The MCV ranges from 55 fL to 75 fL, and the red blood cell count is normal or increased. The reticulocyte count is normal or slightly elevated. The peripheral blood smear is mildly abnormal, with hypochromia, microcytosis, and target cells (eFigure 13–4). In contrast to alpha-thalassemia, basophilic stippling is present. Hemoglobin electrophoresis shows an elevation of hemoglobin A2 to 4–8% and occasional elevations of hemoglobin F to 1–5%.
Beta-thalassemia. (Peripheral blood, 50 ×.) Microcytic red blood cells, most of which are target forms, consistent with beta-thalassemia. These target cells are also hypochromic because they contain very little hemoglobin. (Used, with permission, from L Damon.)
4. Beta-thalassemia intermedia
These patients have a modest anemia with hematocrit between 17% and 33%. The MCV ranges from 55 fL to 75 fL, and the red blood cell count is normal or increased. The reticulocyte count is elevated. The peripheral blood smear is abnormal with hypochromia, microcytosis, basophilic stippling, and target cells. Hemoglobin electrophoresis shows up to 30% hemoglobin A, an elevation of hemoglobin A2 up to 10%, and elevation of hemoglobin F from 6% to 10%.
5. Beta-thalassemia major
These patients have severe anemia, and without transfusion the hematocrit may fall to less than 10%. The peripheral blood smear is bizarre, showing severe poikilocytosis, hypochromia, microcytosis, target cells, basophilic stippling, and nucleated red blood cells. Little or no hemoglobin A is present. Variable amounts of hemoglobin A2 are seen, and the predominant hemoglobin present is hemoglobin F (eFigure 13–5).
Beta-thalassemia major. (Peripheral blood, 50 ×.) Microcytic, hypochromic target cells of severe beta-thalassemia. Many red blood cell shapes are bizarre, consistent with severe thalassemia. There is intense reticulocytosis, as evidenced by a large number of nucleated red blood cells in the peripheral blood. The thalassemias are hyperproductive anemias manifested by hemolysis occurring in the bone marrow compartment due to mispairing of beta and globin units. (Used, with permission, from L Damon.)
Mild forms of thalassemia must be differentiated from iron deficiency. Compared to iron deficiency anemia, patients with thalassemia have a lower MCV, a normal or elevated red blood cell count (rather than low), a more abnormal peripheral blood smear at modest levels of anemia, and usually a reticulocytosis. Iron studies are normal or the transferrin saturation or ferritin (or both) are elevated. Severe forms of thalassemia may be confused with other hemoglobinopathies. The diagnosis of beta-thalassemia is made by the above findings and hemoglobin electrophoresis showing elevated levels of hemoglobins A2 and F (provided the patient is replete in iron), but the diagnosis of alpha-thalassemia is made by exclusion since there is no change in the proportion of the normal adult hemoglobin species. The only other microcytic anemia with a normal or elevated red blood cell count is iron deficiency in a patient with polycythemia vera.
Patients with mild thalassemia (alpha-thalassemia trait or beta-thalassemia minor) require no treatment and should be identified so that they will not be subjected to repeated evaluations and treatment for iron deficiency. Patients with hemoglobin H disease should take folic acid supplementation (1 mg/day orally) and avoid medicinal iron and oxidative drugs such as sulfonamides. Patients with severe thalassemia are maintained on a regular transfusion schedule (in part to suppress endogenous erythropoiesis and therefore bone marrow expansion) and receive folic acid supplementation. Splenectomy is performed if hypersplenism causes a marked increase in the transfusion requirement or refractory symptoms. Patients with regular transfusion requirements should be treated with iron chelation (oral or parenteral) in order to prevent life-limiting organ damage from iron overload.
Allogeneic stem cell transplantation is the treatment of choice for beta-thalassemia major and the only available cure. Children who have not yet experienced organ damage from iron overload do well, with long-term survival in more than 80% of cases.
All patients with severe thalassemia should be referred to a hematologist. Any patient with an unexplained microcytic anemia should be referred to help establish a diagnosis. Patients with thalassemia minor or intermedia should be referred for genetic counseling because offspring of thalassemic couples are at risk for inheriting thalassemia major.
et al. Classification of the disorders of hemoglobin. Cold Spring Harb Perspect Med. 2013 Feb 1;3(2):a011684.
et al. Evidence-based focused review of the status of hematopoietic stem cell transplantation as treatment of sickle cell disease and thalassemia. Blood. 2014 May 15;123(20):3089–94.
et al. 2017 clinical trials update in new treatments of B-thalassemia. Am J Hematol. 2016 Nov;91(11):1135–45.
et al. Allogeneic stem cell transplantation for thalassemia major. Hematol Oncol Clin North Am. 2014 Dec;28(6):1187–200.
D. Thalassemia 2016: modern medicine battles an ancient disease. Am J Hematol. 2016 Jan;91(1):15–21.
The sideroblastic anemias are a heterogeneous group of disorders in which hemoglobin synthesis is decreased because of reduced ability to synthesize heme due to an impaired ability to incorporate iron into protoporphyrin IX. Iron accumulates, particularly in the mitochondria. The disorder is generally acquired; it is most often a subtype of a myelodysplastic syndrome (MDS). Other causes include chronic alcoholism, lead poisoning, copper deficiency, medications (isoniazid and chloramphenicol), and chronic infection or inflammation. Inherited forms are usually X-linked, but rare recessive forms have been documented.
Patients have no specific clinical features other than those related to anemia. The anemia is usually moderate, with hematocrits of 20–30%, but transfusions may occasionally be required. In the sideroblastic subtype of MDS, the MCV is usually normal or slightly increased, as it when due to alcohol. In other types, the MCV is usually low (especially in the inherited forms) leading to confusion with iron deficiency. However, the serum iron level is elevated and the transferrin saturation is high. The peripheral blood smear characteristically shows a dimorphic population of red blood cells, one normal and one microcytic. In cases of lead poisoning, coarse basophilic stippling of the red cells is seen and the serum lead levels will be elevated.
The diagnosis is made by examination of the bone marrow. Characteristically, there is marked erythroid hyperplasia, a sign of ineffective erythropoiesis (expansion of the erythroid compartment of the bone marrow without the release of adequate mature red blood cells into the peripheral blood) (eFigure 13–6). The Prussian blue iron stain of the bone marrow shows a generalized increase in iron stores and the presence of ringed sideroblasts (erythroid cells with iron deposits in mitochrondria encircling the nucleus). Occasionally, the anemia is severe enough to require red blood cell transfusions. These patients usually do not respond well to recombinant erythropoietin therapy, especially when transfusion requirements are significant. There are occasional responses to oral pyridoxine (50–200 mg/day). Removal of offending toxins and drugs is needed in the secondary acquired forms.
Refractory anemia with ringed sideroblasts. (Bone marrow aspirate, 50 ×.) Prussian blue iron stain. There are numerous erythroid precursors with iron-laden mitochondria encircling the nucleus. These are referred to as ringed sideroblasts. When more than 15% of erythroid cells are ringed sideroblasts, the diagnosis of refractory anemia with ringed sideroblasts is established. (Used, with permission, from L Damon.)
A rare form of sideroblastic anemia is now recognized that is due to copper deficiency (hypocupremia). The anemia is normocytic in two-thirds of cases and macrocytic in the remainder. The zinc level is usually elevated. Neutropenia or thrombocytopenia (or both) may also be present. Some patients have a myelopathy or demyelinating peripheral neuropathy. The bone marrow biopsy is usually interpreted as a "myelodysplastic syndrome" due to the presence of ringed sideroblasts and vacuolization of the myeloid and erythroid progenitors. The causes of hypocupremia include excess total body zinc (due to zinc-imbedded dental fillings or excessive oral zinc intake, eg, due to high levels of zinc in some Asian herbal preparations), or gastric bypass surgery. Treatment with copper sulfate (2.5 mg twice daily) is associated with a high hematologic response rate but a low neurologic response rate. Exogenous or endogenous zinc exposure needs to be eliminated.
Refer to a hematologist if diagnostic or transfusion support is needed.
et al. Sideroblastic anemia: diagnosis and management. Hematol Oncol Clin North Am. 2014 Aug;28(4):653–70.
et al. Pathophysiology and genetic mutations in congenital sideroblastic anemia. Pediatr Int. 2013 Dec;55(6):675–9.
et al. Hypocupremia associated cytopenia and myelopathy: a national retrospective review. Eur J Haematol. 2013 Jan;90(1):1–9.
Vitamin B12 belongs to the family of cobalamins and serves as a cofactor for two important reactions in humans (eFigure 13–7). As methylcobalamin, it is a cofactor for methionine synthetase in the conversion of homocysteine to methionine, and as adenosylcobalamin for the conversion of methylmalonyl-coenzyme A (CoA) to succinyl-CoA. These enzymatic steps are critical for annealing Okazaki fragments during DNA synthesis, particularly in erythroid progenitor cells. Vitamin B12 comes from the diet and is present in all foods of animal origin. The daily absorption of vitamin B12 is 5 mcg.
Role of cobalamin (vitamin B12) and folic acid in nucleic acid and myelin metabolism. Lack of either cobalamin or folic acid retards DNA synthesis (A), and lack of cobalamin leads to loss of folic acid, which cannot be held intracellularly unless polyglutamated. Lack of cobalamin also leads to abnormal myelin synthesis, probably via a deficiency in methionine production (B). (Modified and reproduced, with permission, from Chandrasoma P, Taylor CR. Concise Pathology, 3rd ed. Originally published by Appleton & Lange. Copyright © 1998 by The McGraw-Hill Companies, Inc.)
After being ingested, vitamin B12 is bound to intrinsic factor, a protein secreted by gastric parietal cells in an acid environment. Other cobalamin-binding proteins (called R factors) compete with intrinsic factor for vitamin B12. Vitamin B12 bound to R factors cannot be absorbed. The vitamin B12–intrinsic factor complex travels through the intestine and is absorbed in the terminal ileum by cells with specific receptors for the complex. It is then transported through plasma and stored in the liver. Three plasma transport proteins have been identified. Transcobalamins I and III (differing only in carbohydrate structure) are secreted by white blood cells. Although approximately 90% of plasma vitamin B12 circulates bound to transcobalamins I and III, only transcobalamin II is capable of transporting vitamin B12 into cells.
The liver contains 2–5 mg of stored vitamin B12. Since daily utilization is 3–5 mcg, the body usually has sufficient stores of vitamin B12 so that it takes more than 3 years for vitamin B12 deficiency to occur if all intake or absorption immediately ceases.
Since vitamin B12 is present in foods of animal origin, dietary vitamin B12 deficiency is extremely rare but is seen in vegans—strict vegetarians who avoid all dairy products, meat, and fish (Table 13–6). Pernicious anemia is an autoimmune illness whereby autoantibodies destroy gastric parietal cells (that produce intrinsic factor) and cause atrophic gastritis or bind to and neutralize intrinsic factor, or both. Abdominal surgery may lead to vitamin B12 deficiency in several ways. Gastrectomy will eliminate the site of intrinsic factor production; blind loop syndrome will cause competition for vitamin B12 by bacterial overgrowth in the lumen of the intestine; and surgical resection of the ileum will eliminate the site of vitamin B12 absorption. Rare causes of vitamin B12 deficiency include fish tapeworm (Diphyllobothrium latum) infection, in which the parasite uses luminal vitamin B12; pancreatic insufficiency (with failure to inactivate competing cobalamin-binding proteins [R-factors]); and severe Crohn disease, causing sufficient destruction of the ileum to impair vitamin B12 absorption.
Table 13–6.Causes of vitamin B12 deficiency. |Favorite Table|Download (.pdf) Table 13–6. Causes of vitamin B12 deficiency.
Dietary deficiency (rare)
Decreased production or absorption of intrinsic factor
Pernicious anemia (autoimmune)
Helicobacter pylori infection
Competition for vitamin B12 in the gut
Blind loop syndrome
Fish tapeworm (rare)
Decreased ileal absorption of vitamin B12
Transcobalamin II deficiency (rare)
Vitamin B12 deficiency causes a moderate to severe anemia of slow onset; patients may have few symptoms relative to the degree of anemia. In advanced cases, the anemia may be severe, with hematocrits as low as 10–15%, and may be accompanied by leukopenia and thrombocytopenia. The deficiency also produces changes in mucosal cells, leading to glossitis, as well as other vague gastrointestinal disturbances such as anorexia and diarrhea. Vitamin B12 deficiency also leads to a complex neurologic syndrome. Peripheral nerves are usually affected first, and patients complain initially of paresthesias. As the posterior columns of the spinal cord become impaired, patients complain of difficulty with balance or proprioception, or both. In more advanced cases, cerebral function may be altered as well, and on occasion dementia and other neuropsychiatric abnormalities may be present. It is critical to recognize that the nonhematologic manifestations of vitamin B12 deficiency can be manifest despite a completely normal complete blood cell count.
Patients are usually pale and may be mildly icteric or sallow. Typically later in the disease course, neurologic examination may reveal decreased vibration and position sense or memory disturbance (or both).
The diagnosis of vitamin B12 deficiency is made by finding a low serum vitamin B12 (cobalamin) level. Whereas the normal vitamin B12 level is greater than 210 pg/mL (155 pmol/L), most patients with overt vitamin B12 deficiency have serum levels less than 170 pg/mL (126 pmol/L), with symptomatic patients usually having levels less than 100 pg/mL (74 pmol/L). The diagnosis of vitamin B12 deficiency in low or low-normal values (level of 170–210 pg/mL [126–155 pmol/L]) is best confirmed by finding an elevated level of serum methylmalonic acid (greater than 1000 nmol/L) or homocysteine. Of note, elevated levels of serum methylmalonic acid can be due to kidney disease.
The anemia of vitamin B12 deficiency is typically moderate to severe with the MCV quite elevated (110–140 fL). However, it is possible to have vitamin B12 deficiency with a normal MCV from coexistent thalassemia or iron deficiency; in other cases, the reason is obscure. Patients with neurologic symptoms and signs that suggest possible vitamin B12 deficiency should be evaluated for that deficiency despite a normal MCV or the absence of anemia. The peripheral blood smear is megaloblastic, defined as red blood cells that appear as macro-ovalocytes, (although other shape changes are usually present) and neutrophils that are hypersegmented (six [or greater]-lobed neutrophils or mean neutrophil lobe counts greater than four) (eFigures 13–8 and 13–9). The reticulocyte count is reduced. Because vitamin B12 deficiency can affect all hematopoietic cell lines, the white blood cell count and the platelet count are reduced in severe cases.
Vitamin B12 deficiency. (Peripheral blood, 100 ×.) Shown are several hallmark features of vitamin B12 deficiency, including macro-ovalocytes, basophilic stippling, and bizarre-shaped red cell forms. (Used, with permission, from L Damon.)
Vitamin B12 deficiency. (Peripheral blood, 50 ×.) Hypersegmentation of a neutrophil associated with vitamin B12 deficiency. The combination of polymorphonuclear neutrophil nuclear hypersegmentation plus macro-ovalocytes renders the smear megaloblastic, consistent with vitamin B12 or folate deficiency. (Used, with permission, from L Damon.)
Other laboratory abnormalities include elevated serum lactate dehydrogenase (LD) and a modest increase in indirect bilirubin. These two findings are a reflection of intramedullary destruction of developing abnormal erythroid cells and are similar to those observed in peripheral hemolytic anemias.
Bone marrow morphology is characteristically abnormal (eFigure 13–10). Marked erythroid hyperplasia is present as a response to defective red blood cell production (ineffective erythropoiesis). Megaloblastic changes in the erythroid series include abnormally large cell size and asynchronous maturation of the nucleus and cytoplasm—ie, cytoplasmic maturation continues while impaired DNA synthesis causes retarded nuclear development. In the myeloid series, giant bands and meta-myelocytes are characteristically seen.
Vitamin B12 deficiency. (Bone marrow aspirate, 50 ×.) Intense erythroid activity is shown. There is inversion of the usual myeloid-to-erythroid ratio (normally 2–4:1), with predominance of early erythroid cells (pronormoblasts) with deep basophilic cytoplasm. Giant band forms are also present. There is dyssynchrony between nuclear and cytoplasmic maturation—so-called megaloblastic changes. (Used, with permission, from L Damon.)
Vitamin B12 deficiency should be differentiated from folic acid deficiency, the other common cause of megaloblastic anemia, in which red blood cell folic acid is low while vitamin B12 levels are normal. The bone marrow findings of vitamin B12 deficiency are sometimes mistaken for a myelodysplastic syndrome (MDS) or even acute erythrocytic leukemia. The distinction between vitamin B12 deficiency and myelodysplasia is based on the characteristic morphology and the low vitamin B12 and elevated methylmalonic acid levels.
Patients with vitamin B12 deficiency are usually treated with parenteral therapy. Intramuscular or subcutaneous injections of 100 mcg of vitamin B12 are adequate for each dose. Replacement is usually given daily for the first week, weekly for the next month, and then monthly for life. The vitamin deficiency will recur if patients discontinue their therapy. Oral or sublingual methylcobalamin (1 mg/day) may be used instead of parenteral therapy once initial correction of the deficiency has occurred. Oral or sublingual replacement is effective, even in pernicious anemia, since approximately 1% of the dose is absorbed in the intestine via passive diffusion in the absence of active transport. It must be continued indefinitely and serum vitamin B12 levels must be monitored to ensure adequate replacement. For patients with neurologic symptoms caused by vitamin B12 deficiency, long-term parenteral vitamin B12 therapy is prudent. Because many patients are concurrently folic acid deficient from intestinal mucosal atrophy, simultaneous folic acid replacement (1 mg daily) is recommended for the first several months of vitamin B12 replacement.
Patients respond to therapy with an immediate improvement in their sense of well-being. Hypokalemia may complicate the first several days of therapy, particularly if the anemia is severe. A brisk reticulocytosis occurs in 5–7 days, and the hematologic picture normalizes in 2 months. Central nervous system symptoms and signs are reversible if they are of relatively short duration (less than 6 months) but are likely permanent if of longer duration. Red blood cell transfusions are rarely needed despite the severity of anemia, but when given, diuretics are also recommended to avoid heart failure because this anemia develops slowly and the plasma volume is increased.
Referral to a hematologist is not usually necessary.
HF. Vitamin B12
and pernicious anemia—the dawn of molecular medicine. N Engl J Med. 2014 Feb 20;370(8):773–6.
et al. Vitamin B12
deficiency—a 21st century perspective. Clin Med (Lond). 2015 Apr;15(2):145–50.
ESSENTIALS OF DIAGNOSIS
Megaloblastic blood smear (macro-ovalocytes and hypersegmented neutrophils).
Reduced folic acid levels in red blood cells or serum.
Normal serum vitamin B12 level.
“Folic acid” is the term commonly used for pteroylmonoglutamic acid. Folic acid is present in most fruits and vegetables (especially citrus fruits and green leafy vegetables). Daily dietary requirements are 50–100 mcg. Total body stores of folic acid are approximately 5 mg, enough to supply requirements for 2–3 months.
The most common cause of folic acid deficiency is inadequate dietary intake (Table 13–7). Alcoholic or anorectic patients, persons who do not eat fresh fruits and vegetables, and those who overcook their food are candidates for folic acid deficiency. Reduced folic acid absorption is rarely seen, since absorption occurs from the entire gastrointestinal tract. However, medications such as phenytoin, trimethoprim-sulfamethoxazole, or sulfasalazine may interfere with its absorption. Folic acid absorption is poor in some patients with vitamin B12 deficiency due to gastrointestinal mucosal atrophy. Folic acid requirements are increased in pregnancy, hemolytic anemia, and exfoliative skin disease, and in these cases the increased requirements (5 to 10 times normal) may not be met by a normal diet.
Table 13–7.Causes of folic acid deficiency. |Favorite Table|Download (.pdf) Table 13–7. Causes of folic acid deficiency.
Medications: phenytoin, sulfasalazine, trimethoprim-sulfamethoxazole
Concurrent vitamin B12 deficiency
Chronic hemolytic anemia
Exfoliative skin disease
Excess loss: hemodialysis
Inhibition of reduction to active form
The clinical features are similar to those of vitamin B12 deficiency. However, isolated folic acid deficiency does not result in the neurologic abnormalities of vitamin B12 deficiency.
Megaloblastic anemia is identical to anemia resulting from vitamin B12 deficiency. A red blood cell folic acid level below 150 ng/mL (340 nmol/L) is diagnostic of folic acid deficiency. Whether to order a serum or a red blood cell folate level remains unsettled since there are few, if any, data to support one test over the other. Usually the serum vitamin B12 level is normal, and it should always be measured when folic acid deficiency is suspected. In some instances, folic acid deficiency is a consequence of the gastrointestinal mucosal megaloblastosis from vitamin B12 deficiency.
The megaloblastic anemia of folic acid deficiency should be differentiated from vitamin B12 deficiency by the finding of a normal vitamin B12 level and a reduced red blood cell (or serum) folic acid level. Alcoholic patients, who often have nutritional deficiency, may also have anemia of liver disease. Pure anemia of liver disease causes a macrocytic anemia but does not produce megaloblastic morphologic changes in the peripheral blood; rather, target cells are present. Hypothyroidism is associated with mild macrocytosis and also with pernicious anemia.
Folic acid deficiency is treated with daily oral folic acid (1 mg). The response is similar to that seen in the treatment of vitamin B12 deficiency, with rapid improvement and a sense of well-being, reticulocytosis in 5–7 days, and total correction of hematologic abnormalities within 2 months. Large doses of folic acid may produce hematologic responses in cases of vitamin B12 deficiency but permit neurologic damage to progress; hence, obtaining a serum vitamin B12 level in suspected folic acid deficiency is paramount.
Referral to a hematologist is not usually necessary.
et al. Red cell or serum folate: what to do in clinical practice. Clin Chem Lab Med. 2013 Mar 1;51(3):555–69.
BM. Utility of measuring serum or red blood cell folate in the era of folate fortification of flour. Clin Biochem. 2014 May;47(7–8):533–8.
R. Indicators for assessing folate and vitamin B-12 status and for monitoring the efficacy of intervention strategies. Am J Clin Nutr. 2011 Aug;94(2):666S–72S.
Acquired pure red cell aplasia is rare. It is an autoimmune disease mediated either by T lymphocytes or (rarely) by an IgG antibody against erythroid precursors in the bone marrow. In adults, the disease is usually idiopathic. However, cases have been seen in association with systemic lupus erythematosus, chronic lymphocytic leukemia (CLL), lymphomas, or thymoma. Some medications (phenytoin, chloramphenicol) may cause red cell aplasia. Rarely, anti-erythropoietin antibodies cause pure red cell aplasia in patients who are treated with recombinant erythropoietin. Transient episodes of red cell aplasia are probably common in response to viral infections, especially parvovirus infections. However, these acute episodes will go unrecognized unless the patient has a chronic hemolytic disorder or a chronic immunocompromised state, in which case the hematocrit may fall precipitously.
The only signs are those of anemia unless the patient has an associated autoimmune or lymphoproliferative disorder. The anemia is often severe and normochromic, with low or absent reticulocytes. Red blood cell morphology is normal, and the myeloid and platelet lines are unaffected. The bone marrow is normocellular with markedly reduced or absent erythroid progenitors; all non-erythroid elements are present and normal. The bone marrow karyotype is normal on standard banding cytogenetics. In some cases, chest imaging studies will reveal a thymoma.
The disorder must be distinguished from aplastic anemia (in which the marrow is hypocellular and all cell lines are affected) and from myelodysplasia. This latter disorder is recognized by the presence of morphologic abnormalities that should not be present in pure red cell aplasia.
Possible offending medications should be stopped. Most patients will require red blood cell transfusion support. With thymoma, resection alone results in amelioration of anemia in a low proportion of cases (about 10%). High-dose intravenous immune globulin has produced excellent responses in a small number of cases, mainly during parvovirus infections. For idiopathic cases, the treatment of choice is immunosuppressive therapy with a calcineurin inhibitor (ie, cyclosporine) with durable response rates of 65–87%. A calcineurin inhibitor is usually used in conjunction with surgical resection in cases of thymoma. Corticosteroids produce responses in 30–60% of cases, but relapses are common once corticosteroids are discontinued. Anti-CD20 monoclonal antibody (rituximab) is the treatment of choice in the setting of anti-erythropoietin antibodies. In patients with an associated lymphoproliferative disorder, treating the neoplasm should also treat the anemia.
All patients should be referred to a hematologist.
et al. Intravenous immunoglobulin therapy for pure red cell aplasia related to human parvovirus B19 infection: a retrospective study of 10 patients and review of the literature. Clin Infect Dis. 2013 Apr;56(7):968–77.
et al. Antibody-mediated pure red cell aplasia in chronic kidney disease patients receiving erythropoiesis-stimulating agents: new insights. Kidney Int. 2012 Apr;81(8):727–32.
et al. Acquired pure red cell aplasia: updated review of treatment. Br J Haematol. 2008 Aug;142(4):505–15.
The hemolytic anemias are a group of disorders in which red blood cell survival is reduced, either episodically or continuously. The bone marrow has the ability to increase erythroid production up to eightfold in response to reduced red cell survival, so anemia will be present only when the ability of the bone marrow to compensate is outstripped. This will occur when red cell survival is extremely short or when the ability of the bone marrow to compensate is impaired.
Since red blood cell survival is normally 120 days, in the absence of red cell production, the hematocrit will fall at the rate of approximately 1/120 of the hematocrit per day, which translates to a decrease in the hematocrit reading of approximately 2–3% (absolute percentage) per week. For example, a fall of hematocrit from 45% to 36% over 3 weeks need not indicate hemolysis, since this rate of fall would result simply from cessation of red blood cell production. If the hematocrit is falling at a rate faster than that due to decreased production, blood loss or hemolysis is the cause.
Reticulocytosis is an important clue to the presence of hemolysis, since in most hemolytic disorders the bone marrow will respond with increased red blood cell production and earlier release of young red blood cells into the circulation. However, hemolysis can be present without reticulocytosis when a second erythropoietic disorder (infection, nutritional deficiency) is superimposed on hemolysis; in these circumstances, the hematocrit will fall rapidly. Reticulocytosis does not necessarily imply hemolysis, since it also occurs during recovery from hypoproliferative anemia (replacement of a missing nutrient) or acute bleeding. Hemolysis is correctly diagnosed (when acute bleeding and nutrient replacement are excluded) if the hematocrit is either falling or stable despite reticulocytosis.
Hemolytic disorders are generally classified according to whether the defect is intrinsic to the red cell or due to some external factor (Table 13–8). Intrinsic defects have been described in all components of the red blood cell, including the membrane, enzyme systems, and hemoglobin; most of these disorders are hereditary. Hemolytic anemias due to external factors are immune and microangiopathic hemolytic anemias and infections of red blood cells.
Table 13–8.Classification of hemolytic anemias. |Favorite Table|Download (.pdf) Table 13–8. Classification of hemolytic anemias.
Membrane defects: hereditary spherocytosis, hereditary elliptocytosis, paroxysmal nocturnal hemoglobinuria
Glycolytic defects: pyruvate kinase deficiency, severe hypophosphatemia
Oxidation vulnerability: glucose-6-phosphate dehydrogenase deficiency, methemoglobinemia
Hemoglobinopathies: sickle cell syndromes, thalassemia, unstable hemoglobins, methemoglobinemia
Immune: autoimmune, lymphoproliferative disease, drug-induced
Microangiopathic: thrombotic thrombocytopenic purpura, hemolytic-uremic syndrome, disseminated intravascular coagulation, valve hemolysis, metastatic adenocarcinoma, vasculitis, copper overload
Infection: Plasmodium, Clostridium, Borrelia
Certain laboratory features are common to all hemolytic anemias. Haptoglobin, a normal plasma protein that binds and clears free hemoglobin released into plasma, may be depressed in hemolytic disorders. However, the haptoglobin level is influenced by many factors and is not always a reliable indicator of hemolysis, particularly in end-stage liver disease (its site of synthesis). When intravascular hemolysis occurs, transient hemoglobinemia ensues. Hemoglobin is filtered through the glomerulus and is usually reabsorbed by tubular cells. Hemoglobinuria will be present only when the capacity for reabsorption of hemoglobin by renal tubular cells is exceeded. In the absence of hemoglobinuria, evidence for prior intravascular hemolysis is the presence of hemosiderin in shed renal tubular cells (positive urine hemosiderin). With severe intravascular hemolysis, hemoglobinemia and methemalbuminemia may be present. Hemolysis increases the indirect bilirubin, and the total bilirubin may rise to 4 mg/dL (68 mcmol/L) or more. Bilirubin levels higher than this may indicate some degree of hepatic dysfunction. Serum LD levels are strikingly elevated in cases of microangiopathic hemolysis (thrombotic thrombocytopenic purpura, hemolytic-uremic syndrome) and may be elevated in other hemolytic anemias.
Hereditary spherocytosis is a disorder of the red blood cell membrane, leading to chronic hemolytic anemia. Normally, the red blood cell is a biconcave disk with a diameter of 7–8 mcm. The red blood cells must be both strong and deformable—strong to withstand the stress of circulating for 120 days and deformable so as to pass through capillaries 3 mcm in diameter and splenic fenestrations in the cords of the red pulp of approximately 2 mcm. The red blood cell membrane skeleton, made up primarily of the proteins spectrin and actin, gives the red cells these characteristics of strength and deformability.
In hereditary spherocytosis, the membrane defect is an abnormality in spectrin, actin, or other red blood cell membrane proteins, such as band 3 or protein 4.2; these proteins provide most of the scaffolding for the red blood cell membranes. The result is a decrease in surface-to-volume ratio that results in a spherical shape of the red blood cell. These spherical red blood cells are less deformable and unable to pass through the small fenestrations in the splenic red pulp. Hemolysis takes place because of trapping of red blood cells within the spleen and their premature removal by splenic macrophages.
Hereditary spherocytosis is an autosomal dominant disease of variable severity. It is often diagnosed during childhood, but milder cases may be discovered incidentally late in adult life. Anemia may or may not be present, since the bone marrow may be able to compensate for shortened red cell survival. Severe anemia (aplastic crisis) may occur in folic acid deficiency or when bone marrow erythropoiesis is temporarily impaired by infection. Chronic hemolysis causes jaundice and pigment (calcium bilirubinate) gallstones, leading to attacks of cholecystitis. Examination may reveal icterus and a palpable spleen.
The anemia is of variable severity, and the hematocrit may be normal. Reticulocytosis is always present. The peripheral blood smear shows the presence of spherocytes, small cells that have lost their central pallor. Hereditary spherocytosis is the only important disorder associated with microcytosis (sometimes normocytic) and an increased MCHC, often greater than 36 g/dL. As with other hemolytic disorders, there may be an increase in indirect bilirubin. The Coombs test is negative (see section on Autoimmune Hemolytic Anemia).
Because spherocytes are red cells that have lost some membrane surface, they are abnormally vulnerable to swelling induced by hypotonic media. Increased osmotic fragility merely reflects the presence of spherocytes and does not distinguish hereditary spherocytosis from other spherocytic hemolytic disorders such as autoimmune hemolytic anemia. In some laboratories, the osmotic fragility test has been supplanted by ektacytometry, which has the advantages of better reliability and the ability to distinguish spherocytes from other red blood cell abnormalities such as elliptocytes. EMA (eosin-5 maleimide) binding by flow cytometry is another diagnostic tool.
Patients should receive supplementation with daily folic acid, 1 mg. The treatment of choice is splenectomy, which will correct neither the membrane defect nor the spherocytosis but will eliminate the site of hemolysis. The timing of splenectomy is controversial, but certainly after 5 years of life whenever possible and if needed. In mild cases discovered late in adult life, splenectomy may not be necessary.
Patients in whom hereditary spherocytosis is suspected should have the diagnosis confirmed by a hematologist, and decisions regarding splenectomy should be made in consultation with a hematologist.
et al. A pediatrician's practical guide to diagnosing and treating hereditary spherocytosis in neonates. Pediatrics. 2015 Jun;135(6):1107–14.
et al. Hereditary spherocytosis, elliptocytosis, and other red cell membrane disorders. Blood Rev. 2013 Jul;27(4):167–78.
et al. Hereditary spherocytosis: evaluation of 68 children. Indian J Hematol Blood Transfus. 2015 Mar;31(1):127–32.
et al. Long-term follow-up of subtotal splenectomy for hereditary spherocytosis: a single-center study. Blood. 2016 Mar 24;127(12):1616–8.
PAROXYSMAL NOCTURNAL HEMOGLOBINURIA
Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired clonal hematopoietic stem cell disorder that results in abnormal sensitivity of the red blood cell membrane to lysis by complement. The underlying cause is an acquired defect in the gene for phosphatidylinositol class A (PIG-A), which results in a deficiency of the glycosylphosphatidylinositol (GPI) anchor for cellular membrane proteins. In particular, the complement-regulating proteins CD55 and CD59 are deficient, which permits unregulated formation of the complement membrane attack complex on red cell membranes and intravascular hemolysis. Free hemoglobin is released into the blood that scavenges nitric oxide and promotes esophageal spasms, male erectile dysfunction, renal damage, and thrombosis. Patients with significant PNH live about 10–15 years following diagnosis; thrombosis is the primary cause of death.
Classically, patients report episodic hemoglobinuria resulting in reddish-brown urine. Hemoglobinuria is most often noticed in the first morning urine due to the drop in blood pH while sleeping (hypoventilation) that facilitates this hemolysis. Besides anemia, these patients are prone to thrombosis, especially within mesenteric and hepatic veins, central nervous system veins (sagittal vein), and skin vessels (with formation of painful nodules). As this is a hematopoietic stem cell disorder, PNH may appear de novo or arise in the setting of aplastic anemia or myelodysplasia with possible progression to acute myeloid leukemia (AML). It is common that patients with idiopathic aplastic anemia have a small PNH clone (less than 2%) on blood or bone marrow analysis; this should not be considered PNH, especially in the absence of a reticulocytosis or thrombosis.
Anemia is of variable severity and frequency, so reticulocytosis may or may not be present at any given time. Abnormalities on the blood smear are nondiagnostic but may include macro-ovalocytes and polychromasia. Since the episodic hemolysis is mainly intravascular, urine hemosiderin is a useful test. Serum LD is characteristically elevated. Iron deficiency is commonly present, related to chronic iron loss from hemoglobinuria.
The white blood cell count and platelet count may be decreased and are always decreased in the setting of aplastic anemia. The best screening test is flow cytometry of blood erythrocytes, granulocytes, or monocytes to demonstrate deficiency of CD55 and CD59. The proportion of erythrocytes deficient in these proteins might be low due to the ongoing destruction of affected erythrocytes. The FLAER assay (fluorescein-labeled proaerolysin) by flow cytometry is more sensitive. Bone marrow morphology is variable and may show either generalized hypoplasia or erythroid hyperplasia or both. The bone marrow karyotype may be either normal or demonstrate a clonal abnormality.
Many patients with PNH have mild disease not requiring intervention. In severe cases and in those occurring in the setting of myelodysplasia or previous aplastic anemia, allogeneic hematopoietic stem cell transplantation may prove curative. In patients with severe hemolysis (usually requiring red cell transfusions) or thrombosis (or both), treatment with eculizumab is warranted. Eculizumab is a humanized monoclonal antibody against complement protein C5—binding C5 prevents its cleavage so the membrane attack complex cannot assemble. Eculizumab improves quality of life and reduces hemolysis, transfusion requirements, fatigue, and thrombosis risk. Eculizumab is expensive and increases the risk of Neisseria meningitidis infections; patients receiving the antibody must undergo meningococcal vaccination (including vaccines for stain B). Iron replacement is indicated for treatment of iron deficiency when present, which may improve the anemia while also causing a transient increase in hemolysis. For unclear reasons, corticosteroids are effective in decreasing hemolysis.
Most patients with PNH should be under the care of a hematologist.
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et al. Paroxysmal nocturnal hemoglobinuria: from bench to bed. Indian J Hematol Blood Transfus. 2016 Dec;32(4):383–91.
GLUCOSE-6-PHOSPHATE DEHYDROGENASE DEFICIENCY
ESSENTIALS OF DIAGNOSIS
X-linked recessive disorder seen commonly in American black men.
Episodic hemolysis in response to oxidant drugs or infection.
Bite cells and blister cells on the peripheral blood smear.
Reduced levels of glucose-6-phosphate dehydrogenase between hemolytic episodes.
Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a hereditary enzyme defect that causes episodic hemolytic anemia because of the decreased ability of red blood cells to deal with oxidative stresses. G6PD deficiency leads to excess oxidized glutathione (hence, inadequate levels of reduced glutathione) that forces hemoglobin to denature and form precipitants called Heinz bodies. Heinz bodies cause red blood cell membrane damage, which leads to premature removal of these red blood cells by reticuloendothelial cells within the spleen (extravascular hemolysis).
Numerous G6PD isoenzymes have been described. The usual isoenzyme found in American blacks is designated G6PD-A and that found in whites is designated G6PD-B, both of which have normal function and stability and therefore no hemolytic anemia. Ten to 15 percent of American blacks have the variant G6PD isoenzyme designated A–, in which there is both a reduction in normal enzyme activity and a reduction in its stability. The A– isoenzyme activity declines rapidly as the red blood cell ages past 40 days, a fact that explains the clinical findings in this disorder. More than 150 G6PD isoenzyme variants have been described, including some Mediterranean, Ashkenazi Jewish, and Asian variants with very low enzyme activity, episodic hemolysis, and exacerbations due to oxidizing substances including fava beans (class II G6PD activity). The other classes of G6PD isoenzyme activity are class I, extremely low activity with associated chronic, severe hemolysis; class III, 10–60% activity with episodic hemolysis (includes the American black A– isoform); class IV, 60–150% activity (normal); and class V, greater than 150% activity. Patients with G6PD deficiency seem to be protected from malaria parasitic infection, have less coronary artery disease, and possibly have fewer cancers and greater longevity.
G6PD deficiency is an X-linked disorder affecting 10–15% of American hemizygous black males and rare female homozygotes. Female carriers are rarely affected—only when an unusually high percentage of cells producing the normal enzyme are X-inactivated.
Patients are usually healthy, without chronic hemolytic anemia or splenomegaly. Hemolysis occurs episodically as a result of oxidative stress on the red blood cells, generated either by infection or exposure to certain medications. Medications initiating hemolysis that should be avoided include dapsone, methylene blue, phenazopyridine, primaquine, rasburicase, toluidine blue, nitrofurantoin, trimethoprim/sulfamethoxazole, sulfadiazine, and quinolones. Other medications, such as chloroquine, quinine, high-dose aspirin, and isoniazid, have been implicated but are less certain as offenders since they are often given during infections. Even with continuous use of the offending medication, the hemolytic episode is self-limited because older red blood cells (with low enzyme activity) are removed and replaced with a population of young red blood cells (reticulocytes) with adequate functional levels of G6PD. Severe G6PD deficiency (as in Mediterranean variants) may produce a chronic hemolytic anemia.
Between hemolytic episodes, the blood is normal. During episodes of hemolysis, the hemoglobin rarely falls below 8 g/dL (80 g/L), and there is reticulocytosis and increased serum indirect bilirubin. The peripheral blood cell smear often reveals a small number of “bite” cells—cells that appear to have had a bite taken out of their periphery, or “blister” cells (eFigure 13–11). This indicates pitting of precipitated membrane hemoglobin aggregates by the splenic macrophages. Heinz bodies may be demonstrated by staining a peripheral blood smear with cresyl violet (eFigure 13–12); they are not visible on the usual Wright-Giemsa–stained blood smear. Specific enzyme assays for G6PD reveal a low level but may be falsely normal if they are performed during or shortly after a hemolytic episode during the period of reticulocytosis. In these cases, the enzyme assays should be repeated weeks after hemolysis has resolved. In severe cases of G6PD deficiency, enzyme levels are always low.
Glucose-6-phosphate dehydrogenase (G6PD) deficiency. (Peripheral blood smear, 100 ×.) Several features of G6PD deficiency in the setting of an oxidative challenge are shown. The polychromatophils (large, bluish young red blood cells) and nucleated red blood cells indicate the current hemolytic state. Also shown are "bite" cells, which are red blood cell morphologic changes that are the consequence of macrophage action on the Heinz bodies, which have precipitated in the inner leaflet of the red blood cell membranes. (Used, with permission, from L Damon.)
Heinz bodies. (Peripheral blood, 100 ×.) Brilliant cresyl blue stain. Areas of precipitated hemoglobin are seen on the inner leaflet of the red blood cell membrane. These precipitations are called Heinz bodies and are the consequence of hemoglobin oxidation and denaturation. Severe oxidative stress can result in abnormal red blood cell membrane deformability and subsequent extravascular hemolysis. (Used, with permission, from L Damon.)
No treatment is necessary except to avoid known oxidant medications.
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et al. Glucose-6-phosphate dehydrogenase deficiency: disadvantages and possible benefits. Cardiovasc Hematol Disord Drug Targets. 2013 Mar 1;13(1):73–82.
SICKLE CELL ANEMIA & RELATED SYNDROMES
ESSENTIALS OF DIAGNOSIS
Recurrent pain episodes.
Positive family history and lifelong history of hemolytic anemia.
Irreversibly sickled cells on peripheral blood smear.
Hemoglobin S is the major hemoglobin seen on electrophoresis.
Sickle cell anemia is an autosomal recessive disorder in which an abnormal hemoglobin leads to chronic hemolytic anemia with numerous clinical consequences. A single DNA base change leads to an amino acid substitution of valine for glutamine in the sixth position on the beta-globin chain. The abnormal beta chain is designated betas and the tetramer of alpha-2betas-2 is designated hemoglobin S (eFigure 13–13). Hemoglobin S is unstable and polymerizes in the setting of various stressors, including hypoxemia and acidosis, leading to the formation of sickled red blood cells. Sickled cells result in hemolysis and the release of ATP, which is converted to adenosine. Adenosine binds to its receptor (A2B) resulting in the production of 2,3-biphosphoglycerate and the induction of more sickling and to its receptor (A2A) on natural killer cells resulting in pulmonary inflammation. The free hemoglobin from hemolysis scavenges nitric oxide causing endothelial dysfunction, vascular injury, and pulmonary hypertension.
Hemoglobin SS disease. (Peripheral blood, 50 ×.) Multiple sickled forms are the consequence of hemoglobin S polymerization. Also present are target cells—a manifestation of either sickle cell hepatopathy or concomitant sickle-beta thalassemia. (Used, with permission, from L Damon.)
The rate of sickling is influenced by the intracellular concentration of hemoglobin S and by the presence of other hemoglobins within the cell. Hemoglobin F cannot participate in polymer formation, and its presence markedly retards sickling. Factors that increase sickling are red blood cell dehydration and factors that lead to formation of deoxyhemoglobin S (eg, acidosis and hypoxemia) either systemic or local in tissues. Hemolytic crises may be related to splenic sequestration of sickled cells (primarily in childhood before the spleen has been infarcted as a result of repeated sickling) or with coexistent disorders such as G6PD deficiency.
The betaS gene is carried in 8% of American blacks, and 1 of 400 American black children will be born with sickle cell anemia. Prenatal diagnosis is available for couples at risk for producing a child with sickle cell anemia. Genetic counseling should be made available to such couples.
The disorder has its onset during the first year of life, when hemoglobin F levels fall as a signal is sent to switch from production of gamma-globin to beta-globin. Chronic hemolytic anemia produces jaundice, pigment (calcium bilirubinate) gallstones, splenomegaly (early in life), and poorly healing ulcers over the lower tibia. Life-threatening severe anemia can occur during hemolytic or aplastic crises, the latter generally associated with viral or other infection or by folic acid deficiency causing reduced erythropoiesis.
Acute painful episodes due to acute vaso-occlusion from clusters of sickled red cells may occur spontaneously or be provoked by infection, dehydration, or hypoxia. Common sites of acute painful episodes include the spine and long appendicular and thoracic bones. These episodes last hours to days and may produce low-grade fever. Acute vaso-occlusion may cause strokes due to sagittal sinus venous thrombosis or to bland or hemorrhagic central nervous system arterial ischemia and may also cause priapism. Vaso-occlusive episodes are not associated with increased hemolysis.
Repeated episodes of vascular occlusion especially affect the heart, lungs, and liver. The acute chest syndrome is characterized by acute chest pain, hypoxemia and pulmonary infiltrates on a chest radiograph and must be distinguished from an infectious pneumonia. Ischemic necrosis of bone occurs, rendering the bone susceptible to osteomyelitis due to salmonellae and (somewhat less commonly) staphylococci. Infarction of the papillae of the renal medulla causes renal tubular concentrating defects and gross hematuria, more often encountered in sickle cell trait than in sickle cell anemia. Retinopathy similar to that noted in diabetes mellitus is often present and may lead to visual impairment. Pulmonary hypertension may develop and is associated with a poor prognosis. These patients are prone to delayed puberty. An increased incidence of infection is related to hyposplenism as well as to defects in the alternate complement pathway.
On examination, patients are often chronically ill and jaundiced. There is hepatomegaly, but the spleen is not palpable in adult life. The heart is enlarged, with a hyperdynamic precordium and systolic murmurs. Nonhealing ulcers of the lower leg and retinopathy may be present.
Sickle cell anemia becomes a chronic multisystem disease, with death from organ failure. With improved supportive care, average life expectancy is now between 40 and 50 years of age.
Chronic hemolytic anemia is present. The hematocrit is usually 20–30%. The peripheral blood smear is characteristically abnormal, with irreversibly sickled cells comprising 5–50% of red cells. Other findings include reticulocytosis (10–25%), nucleated red blood cells, and hallmarks of hyposplenism such as Howell-Jolly bodies and target cells (eFigure 13–14). The white blood cell count is characteristically elevated to 12,000–15,000/mcL, and reactive thrombocytosis may occur. Indirect bilirubin levels are high.
Hemoglobin SS disease. (Peripheral blood, 100 ×.) Sickled red blood cells and target cells in a patient with hemoglobin SS disease and sickle hepatopathy. In addition, the red blood cell in the lower central area of the field contains a hard peripheral inclusion called a Howell-Jolly body. This represents nuclear remnants and is the consequence of hyposplenism. (Used, with permission, from L Damon.)
After a screening test for sickle cell hemoglobin, the diagnosis of sickle cell anemia is confirmed by hemoglobin electrophoresis (Table 13–9). Hemoglobin S will usually comprise 85–98% of hemoglobin. In homozygous S disease, no hemoglobin A will be present. Hemoglobin F levels are variably increased, and high hemoglobin F levels are associated with a more benign clinical course. Patients with S-beta+-thalassemia and SS alpha-thalassemia also have a more benign clinical course than sickle cell anemia (SS) patients.
Table 13–9.Hemoglobin distribution in sickle cell syndromes. |Favorite Table|Download (.pdf) Table 13–9. Hemoglobin distribution in sickle cell syndromes.
|Genotype ||Clinical Diagnosis ||Hb A ||Hb S ||Hb A2 ||Hb F |
|AA ||Normal ||97–99% ||0% ||1–2% ||< 1% |
|AS ||Sickle trait ||60% ||40% ||1–2% ||< 1% |
|AS, alpha-thalassemia ||Sickle trait, alpha-thalassemia ||70–75% ||25–30% ||1–2% ||< 1% |
|SS ||Sickle cell anemia ||0% ||86–98% ||1–3% ||5–15% |
|SS, alpha-thalassemia (3 genes) ||SS alpha-thalassemia, silent ||0% ||90% ||3% ||7–9% |
|SS, alpha-thalassemia (2 genes) ||SS alpha-thalassemia, trait ||0% ||80% ||3% ||11–21% |
|S, beta0-thalassemia ||Sickle beta0-thalassemia ||0% ||70–80% ||3–5% ||10–20% |
|S, beta+-thalassemia ||Sickle beta+-thalassemia ||10–20% ||60–75% ||3–5% ||10–20% |
When allogeneic hematopoietic stem cell transplantation is performed before the onset of significant end-organ damage, it can cure more than 80% of children with sickle cell anemia who have suitable HLA-matched donors. Transplantation remains investigational in adults. Other therapies modulate disease severity: cytotoxic agents, such as hydroxyurea, increase hemoglobin F levels epigenetically. Hydroxyurea (500–750 mg orally daily) reduces the frequency of painful crises in patients whose quality of life is disrupted by frequent pain crises (three or more per year). Long-term follow-up of patients taking hydroxyurea demonstrates it improves overall survival and quality of life with little evidence for secondary malignancy. The use of omega-3 (n-3) fatty acid supplementation may reduce vaso-occlusive episodes and reduce transfusion needs in patients with sickle cell anemia.
Supportive care is the mainstay of treatment for sickle cell anemia. Patients are maintained on folic acid supplementation (1 mg orally daily) and given transfusions for aplastic or hemolytic crises. When acute painful episodes occur, precipitating factors should be identified and infections treated if present. The patient should be kept well hydrated, given generous analgesics, and supplied oxygen if hypoxic. Pneumococcal vaccination reduces the incidence of infections with this pathogen. Angiotensin-converting enzyme inhibitors are recommended in patients with microalbuminuria.
Exchange transfusions are indicated for the treatment of severe acute vaso-occlusive crises, intractable pain crises, acute chest syndrome, priapism, and stroke. Long-term transfusion therapy has been shown to be effective in reducing the risk of recurrent stroke in children. It has been recommended that children with SS who are aged 2–16 years have annual transcranial ultrasounds and, if the Doppler velocity is abnormal (200 cm/s or greater), the clinician should strongly consider beginning transfusions to prevent stroke. Iron chelation is needed for those on chronic transfusion therapy.
Patients with sickle cell anemia should have their care coordinated with a hematologist and should be referred to a Comprehensive Sickle Cell Center, if one is available.
Patients should be admitted for management of acute chest crises, for aplastic crisis, or for painful episodes that do not respond to outpatient care.
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People with the heterozygous hemoglobin genotype AS have sickle cell trait. These persons are hematologically normal, with no anemia and normal red blood cells on peripheral blood smear. A screening test for sickle hemoglobin will be positive, and hemoglobin electrophoresis will reveal that approximately 40% of hemoglobin is hemoglobin S (Table 13–9). People with sickle cell trait experience more rhabdomyolysis during vigorous exercise but do not have increased mortality compared to the general population. They may be at increased risk for venous thromboembolism. Chronic sickling of red blood cells in the acidotic renal medulla results in microscopic and gross hematuria, hyposthenuria (poor urine concentrating ability), and possibly chronic kidney disease. No treatment is necessary but genetic counseling is recommended.
et al. Prospective study of sickle cell trait and venous thromboembolism incidence. J Thromb Haemost. 2015 Jan;13(1):2–9.
et al. Sickle cell trait, rhabdomyolysis, and mortality among U.S. Army soldiers. N Engl J Med. 2016 Aug 4;375(5):435–42.
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Patients with homozygous sickle cell anemia and alpha-thalassemia have less vigorous hemolysis and run higher hemoglobins than SS patients due to reduced red blood cell sickling related to a lower hemoglobin concentration within the red blood cell and higher hemoglobin F levels (Table 13–9). The MCV is low, and the red cells are hypochromic.
Patients who are compound heterozygotes for betas and beta-thalassemia are clinically affected with sickle cell syndromes. Sickle beta0-thalassemia is clinically very similar to homozygous SS disease. Vaso-occlusive crises may be somewhat less severe, and the spleen is not always infarcted. The MCV is low, in contrast to the normal MCV of sickle cell anemia. Hemoglobin electrophoresis reveals no hemoglobin A but will show an increase in hemoglobins A2 and F (Table 13–9).
Sickle beta+-thalassemia is a milder disorder than homozygous SS disease, with fewer pain episodes but more acute chest syndrome than sickle beta0-thalassemia. The spleen is usually palpable. The hemolytic anemia is less severe, and the hematocrit is usually 30–38%, with reticulocytes of 5–10%. Hemoglobin electrophoresis shows the presence of some hemoglobin A and elevated hemoglobins A2 and F (Table 13–9). The MCV is low.
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et al. Transfusional iron overload and iron chelation therapy in thalassemia major and sickle cell disease. Hematol Oncol Clin North Am. 2014 Aug;28(4):703–27.
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Hemoglobin C is formed by a single amino acid substitution at the same site as in sickle hemoglobin (codon 6 of the beta globin gene) but with lysine instead of valine substituted for glutamine. Hemoglobin C is nonsickling but may participate in polymer formation in association with hemoglobin S. Homozygous hemoglobin C disease produces a mild hemolytic anemia with splenomegaly, mild jaundice, and pigment (calcium bilirubinate) gallstones. The peripheral blood smear shows generalized red cell targeting and occasional cells with angular crystals of hemoglobin C (eFigure 13–15). Persons heterozygous for hemoglobin C are clinically normal.
Hemoglobin CC disease. (Peripheral blood, 50 ×.) Many red blood cells with crystalline central inclusions of polymerized C hemoglobin. Note that no sickled forms are present, as this is not a sickling disorder. (Used, with permission, from L Damon.)
Patients with hemoglobin SC disease are compound heterozygotes for betaS and betaC. These patients, like those with sickle beta+-thalassemia, have a milder hemolytic anemia and milder clinical course than those with homozygous SS disease and they live longer. There are fewer vaso-occlusive events, and the spleen remains palpable in adult life. However, persons with hemoglobin SC disease have more retinopathy and more priapism than those with SS disease. The hematocrit is usually 30–38%, with 5–10% reticulocytes, and compared to SS, fewer irreversibly sickled cells on the blood smear. Target cells are more numerous than in SS disease. Hemoglobin electrophoresis will show approximately 45–50% hemoglobin C, 50% hemoglobin S, and no increase in hemoglobin F levels.
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Unstable hemoglobins are prone to oxidative denaturation even in the presence of a normal G6PD system. The disorder is autosomal dominant and of variable severity. Most patients have a mild chronic hemolytic anemia with splenomegaly, mild jaundice, and pigment (calcium bilirubinate) gallstones. Less severely affected patients are not anemic except under conditions of oxidative stress.
The diagnosis is suspected by the finding of Heinz bodies combined with a normal G6PD level when checked during a period of hemolytic quiescence. Hemoglobin electrophoresis is usually normal, since these hemoglobins characteristically do not have a change in their migration pattern. These hemoglobins precipitate in isopropanol. Usually no treatment is necessary. Patients with chronic hemolytic anemia should receive folic acid supplementation (1 mg orally) and avoid known oxidative drugs. In rare cases, splenectomy may be required.
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AUTOIMMUNE HEMOLYTIC ANEMIA
ESSENTIALS OF DIAGNOSIS
Acquired hemolytic anemia caused by IgG autoantibody.
Spherocytes and reticulocytosis on peripheral blood smear.
Positive antiglobulin (Coombs) test.
Autoimmune hemolytic anemia is an acquired disorder in which an IgG autoantibody is formed that binds to a red blood cell membrane protein and does so most avidly at body temperature (ie, a “warm” autoantibody). The antibody is most commonly directed against a basic component of the Rh system present on most human red blood cells. When IgG antibodies coat the red blood cell, the Fc portion of the antibody is recognized by macrophages present in the spleen and other portions of the reticuloendothelial system. The interaction between splenic macrophages and the antibody-coated red blood cell results in removal of red blood cell membrane and the formation of a spherocyte due to the decrease in surface-to-volume ratio of the surviving red blood cell. These spherocytic cells have decreased deformability and are unable to squeeze through the 2-mcm fenestrations of splenic sinusoids and become trapped in the red pulp of the spleen. When large amounts of IgG are present on red blood cells, complement may be fixed. Direct complement lysis of cells is rare, but the presence of C3b on the surface of red blood cells allows Kupffer cells in the liver to participate in the hemolytic process via C3b receptors. The destruction of red blood cells in the spleen and liver designates this as extravascular hemolysis.
Approximately one-half of all cases of autoimmune hemolytic anemia are idiopathic. The disorder may also be seen in association with systemic lupus erythematosus, other rheumatic disorders, chronic lymphocytic leukemia (CLL), or lymphomas. It must be distinguished from drug-induced hemolytic anemia. When penicillin (or other medications, especially cefotetan, ceftriaxone, and piperacillin) coats the red blood cell membrane, the autoantibody is directed against the membrane-drug complex. Fludarabine, an antineoplastic, causes autoimmune hemolytic anemia through its immunosuppression effects resulting in defective self- versus non-self-immune surveillance permitting the escape of a B-cell clone, which produces the offending autoantibody.
Autoimmune hemolytic anemia typically produces an anemia of rapid onset that may be life-threatening. Patients complain of fatigue and dyspnea and may present with angina pectoris or heart failure. On examination, jaundice and splenomegaly are usually present.
The anemia is of variable degree but may be very severe, with hematocrit of less than 10%. Reticulocytosis is present, and spherocytes are seen on the peripheral blood smear. In cases of severe hemolysis, the stressed bone marrow may also release nucleated red blood cells (eFigure 13–16). As with other hemolytic disorders, the serum indirect bilirubin is increased and the haptoglobin is low. Approximately 10% of patients with autoimmune hemolytic anemia have coincident immune thrombocytopenia (Evans syndrome).
Warm autoimmune hemolytic anemia. (Peripheral blood, 50 ×.) Intense microspherocytosis, one of the hallmarks of autoimmune hemolytic anemia due to a warm autoantibody. Also shown is polychromatophilia (large, slightly blue erythrocytes) representing an intense reticulocytosis system removing bits of immunoglobulin-coated red blood cell membrane. (Used, with permission, from L Damon.)
The antiglobulin (Coombs) test forms the basis for diagnosis. The Coombs reagent is a rabbit IgM antibody raised against human IgG or human complement. The direct antiglobulin (Coombs) test (DAT) is performed by mixing the patient’s red blood cells with the Coombs reagent and looking for agglutination, which indicates the presence of antibody or complement or both on the red blood cell surface. The indirect antiglobulin (Coombs) test is performed by mixing the patient’s serum with a panel of type O red blood cells. After incubation of the test serum and panel red blood cells, the Coombs reagent is added. Agglutination in this system indicates the presence of free antibody (autoantibody or alloantibody) in the patient’s serum.
The direct antiglobulin test is positive (for IgG, complement, or both) in about 90% of patients with autoimmune hemolytic anemia. The indirect antiglobulin test may or may not be positive. A positive indirect antiglobulin test indicates the presence of a large amount of autoantibody that has saturated binding sites in the red blood cell and consequently appears in the serum. Because the patient’s serum usually contains the autoantibody, it may be difficult to obtain a “compatible” cross-match with homologous red blood cells for transfusions since the cross-match indicates the possible presence (true or false) of a red blood cell “alloantibody.”
Initial treatment consists of prednisone, 1–2 mg/kg/day orally in divided doses. Patients with DAT-negative and DAT-positive autoimmune hemolysis respond equally well to corticosteroids. Transfused red blood cells will survive similarly to the patient’s own red blood cells. Because of difficulty in performing the cross-match, possible “incompatible” blood may need to be given. Decisions regarding transfusions should be made in consultation with a hematologist and a blood bank specialist. Death from cardiovascular collapse can occur in the setting of rapid hemolysis. In patients with rapid hemolysis, therapeutic plasmapheresis should be performed early in management to remove autoantibodies. If prednisone is ineffective or if the disease recurs on tapering the dose, splenectomy should be considered. Splenectomy may cure the disorder. Patients with autoimmune hemolytic anemia refractory to prednisone and splenectomy may also be treated with a variety of agents. Treatment with rituximab, a monoclonal antibody against the B cell antigen CD20, is effective in some cases. The suggested dose is 375 mg/m2 intravenously weekly for 4 weeks. Rituximab is used in conjunction with corticosteroids as initial therapy in some patients with severe disease. Danazol, 400–800 mg/day orally, is less often effective than in immune thrombocytopenia but is well suited for long-term use because of its low toxicity profile. Immunosuppressive agents, including cyclophosphamide, vincristine, azathioprine, mycophenolate mofetil, alemtuzumab (an anti-CD52 antibody), or cyclosporine, may also be used. High-dose intravenous immune globulin (1 g/kg daily for 2 days) may be effective in controlling hemolysis. The benefit is short-lived (1–3 weeks), and the medication is very expensive. The long-term prognosis for patients with this disorder is good, especially if there is no other underlying autoimmune disorder or lymphoproliferative disorder. Treatment of an associated lymphoproliferative disorder will also treat the hemolytic anemia.
Patients with autoimmune hemolytic anemia should be referred to a hematologist for confirmation of the diagnosis and subsequent care.
Patients should be hospitalized for symptomatic anemia or rapidly falling hemoglobin levels.
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et al. Characterization of direct antiglobulin test-negative autoimmune hemolytic anemia: a study of 154 cases. Am J Hematol. 2013 Feb;88(2):93–6.
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ESSENTIALS OF DIAGNOSIS
Increased reticulocytes on peripheral blood smear.
Antiglobulin (Coombs) test positive only for complement.
Positive cold agglutinin titer.
Cold agglutinin disease is an acquired hemolytic anemia due to an IgM autoantibody (called a “cold agglutinin”) usually directed against the I/i antigen on red blood cells. These IgM autoantibodies characteristically will react poorly with cells at 37°C but avidly at lower temperatures, usually at 0–4°C (ie, “cold” autoantibody). Since the blood temperature (even in the most peripheral parts of the body) rarely goes lower than 20°C, only cold autoantibodies reactive at relatively higher temperatures will produce clinical effects. Hemolysis results indirectly from attachment of IgM, which in the cooler parts of the circulation (fingers, nose, ears) binds and fixes complement. When the red blood cell returns to a warmer temperature, the IgM antibody dissociates, leaving complement on the cell. Complement lysis of red blood cells rarely occurs. Rather, C3b, present on the red blood cells, is recognized by Kupffer cells (which have receptors for C3b), and red blood cell sequestration and destruction in the liver ensues (extravascular hemolysis). In some cases, the complement membrane attack complex forms, lysing the red blood cells (intravascular hemolysis).
Most cases of chronic cold agglutinin disease are idiopathic. Others occur in association with Waldenström macroglobulinemia, lymphoma, or CLL, in which a monoclonal IgM paraprotein is produced. Acute postinfectious cold agglutinin disease occurs following mycoplasmal pneumonia or viral infection (infectious mononucleosis, measles, mumps, or cytomegalovirus [CMV] with autoantibody directed against antigen i rather than I).
In chronic cold agglutinin disease, symptoms related to red blood cell agglutination occur on exposure to cold, and patients may complain of mottled or numb fingers or toes, acrocyanosis, episodic low back pain, and dark-colored urine. Hemolytic anemia is occasionally severe, but episodic hemoglobinuria may occur on exposure to cold. The hemolytic anemia in acute postinfectious syndromes is rarely severe.
Mild anemia is present with reticulocytosis and rarely spherocytes. The blood smear made at room temperature shows agglutinated red blood cells (there is no agglutination on a blood smear made at body temperature). The direct antiglobulin (Coombs) test will be positive for complement only. Serum cold agglutinin titer will semi-quantitate the autoantibody. A monoclonal IgM is often found on serum protein electrophoresis and confirmed by serum immunoelectrophoresis. There is indirect hyperbilirubinemia and the haptoglobin is low during periods of hemolysis.
Treatment is largely symptomatic, based on avoiding exposure to cold. Splenectomy and prednisone are usually ineffective (except when associated with a lymphoproliferative disorder) since hemolysis takes place in the liver and blood stream. Rituximab is the treatment of choice. The dose is 375 mg/m2 intravenously weekly for 4 weeks. Relapses may be effectively re-treated. High-dose intravenous immunoglobulin (2 g/kg) may be effective temporarily, but it is rarely used because of the high cost and short duration of benefit. Patients with severe disease may be treated with cytotoxic agents, such as cyclophosphamide, fludarabine, or bortezomib, or with immunosuppressive agents, such as cyclosporine. As in warm IgG-mediated autoimmune hemolysis, it may be difficult to find compatible blood for transfusion. Red blood cells should be transfused through an in-line blood warmer.
W. Immune hemolysis: diagnosis and treatment recommendations. Semin Hematol. 2015 Oct;52(4):304–12.
et al. Cold agglutinin-mediated autoimmune hemolytic anemia. Hematol Oncol Clin North Am. 2015 Jun;29(3):455–71.
et al. The role of complement activation in thrombosis and hemolytic anemias. Transfus Apher Sci. 2016 Apr;54(2):191–8.
MICROANGIOPATHIC HEMOLYTIC ANEMIAS
The microangiopathic hemolytic anemias are a group of disorders in which red blood cell fragmentation takes place. The anemia is intravascular, producing hemoglobinemia, hemoglobinuria and, in severe cases, methemalbuminemia. The hallmark of the disorder is the finding of fragmented red blood cells (schistocytes, helmet cells) on the peripheral blood smear (eFigure 13–17).
Hemolytic-uremic syndrome. (Peripheral blood, 50 ×.) Shown are multiple schistocytes (fractured red blood cells), pathognomonic of microangiopathic hemolytic disorders such as hemolytic-uremic syndrome and thrombotic thrombocytopenic purpura. This is a hemolytic state, as evidenced by an increased reticulocyte count and very often the presence of polychromasia (immature, slightly blue erythrocytes). Very few platelets are present. (Used, with permission, from L Damon.)
These fragmentation syndromes can be caused by a variety of disorders (Table 13–8). Thrombotic thrombocytopenic purpura and hemolytic-uremic syndrome are the most important of these and is discussed in Chapter 14. Clinical features are variable and depend on the underlying disorder. Thrombocytopenia is uniformly present. Coagulopathy is variably present and depends on the underlying disorder driving the microangiopathy.
Chronic microangiopathic hemolytic anemia (such as is present with a malfunctioning cardiac valve prosthesis) may cause iron deficiency anemia because of continuous low-grade hemoglobinuria.
et al. Advances and challenges in the management of complement-mediated thrombotic microangiopathies. Ther Adv Hematol. 2015 Aug;6(4):171–85.
et al. The complex differential diagnosis between thrombotic thrombocytopenic purpura and the atypical hemolytic uremic syndrome: laboratory weapons and their impact on treatment choice and monitoring. Thromb Res. 2015 Nov;136(5):851–4.
Aplastic anemia is a condition of bone marrow failure that arises from suppression of, or injury to, the hematopoietic stem cell. The bone marrow becomes hypoplastic, fails to produce mature blood cells, and pancytopenia develops.
There are a number of causes of aplastic anemia (Table 13–10). Direct hematopoietic stem cell injury may be caused by radiation, chemotherapy, toxins, or pharmacologic agents. Systemic lupus erythematosus may rarely cause suppression of the hematopoietic stem cell by an IgG autoantibody directed against the hematopoietic stem cell. However, the most common pathogenesis of aplastic anemia appears to be autoimmune suppression of hematopoiesis by a T-cell-mediated cellular mechanism, so called idiopathic aplastic anemia. In some cases of idiopathic aplastic anemia, defects in maintenance of the hematopoietic stem cell telomere length (dyskeratosis congenita) or in DNA repair pathways (Fanconi anemia) have been identified and are likely linked to both the initiation of bone marrow failure and the propensity to later progress to myelodysplasia, PNH, or AML. Complex detrimental immune responses to viruses can also cause aplastic anemia.
Table 13–10.Causes of aplastic anemia. |Favorite Table|Download (.pdf) Table 13–10. Causes of aplastic anemia.
Autoimmune: idiopathic, systemic lupus erythematosus
Congenital: defects in telomere length maintenance or DNA repair (rare)
Toxins: benzene, toluene, insecticides
Medications: chloramphenicol, gold salts, sulfonamides, phenytoin, carbamazepine, quinacrine, tolbutamide
Post-viral hepatitis (A, B, C, E, G, non-A through -G)
Non-hepatitis viruses (EBV, parvovirus, CMV, echovirus 3, others)
Paroxysmal nocturnal hemoglobinuria
Patients come to medical attention because of the consequences of bone marrow failure. Anemia leads to symptoms of weakness and fatigue, neutropenia causes vulnerability to bacterial or fungal infections, and thrombocytopenia results in mucosal and skin bleeding. Physical examination may reveal signs of pallor, purpura, and petechiae (eFigure 13–18). Other abnormalities such as hepatosplenomegaly, lymphadenopathy, or bone tenderness should not be present, and their presence should lead to questioning the diagnosis.
Nonpalpable purpura. (Reproduced, with permission, from Bondi EE, Jegasothy BV, Lazarus GS [editors]. Dermatology: Diagnosis & Treatment. Originally published by Appleton & Lange. Copyright © 1991 by The McGraw-Hill Companies, Inc.)
The hallmark of aplastic anemia is pancytopenia. However, early in the evolution of aplastic anemia, only one or two cell lines may be reduced.
Anemia may be severe and is always associated with reticulocytopenia. Red blood cell morphology is unremarkable, but there may be mild macrocytosis (increased MCV). Neutrophils and platelets are reduced in number, and no immature or abnormal forms are seen on the blood smear. The bone marrow aspirate and the bone marrow biopsy appear hypocellular, with only scant amounts of morphologically normal hematopoietic progenitors. The prior dictum that the bone marrow karyotype should be normal (or germline if normal variant) has evolved and some clonal abnormalities or other genetic aberrations may be present even in the setting of idiopathic aplastic anemia.
Aplastic anemia must be differentiated from other causes of pancytopenia (Table 13–11). Hypocellular forms of myelodysplasia or acute leukemia may occasionally be confused with aplastic anemia. These are differentiated by the presence of cellular morphologic abnormalities, increased percentage of blasts, or abnormal karyotype in bone marrow cells typical of MDS or acute leukemia. Hairy cell leukemia has been misdiagnosed as aplastic anemia and should be recognized by the presence of splenomegaly and by abnormal “hairy” lymphoid cells in a hypocellular bone marrow biopsy. Pancytopenia with a normocellular bone marrow may be due to systemic lupus erythematosus, disseminated infection, hypersplenism, nutritional (eg, vitamin B12 or folate) deficiency, or myelodysplasia. Isolated thrombocytopenia may occur early as aplastic anemia develops and may be confused with immune thrombocytopenia.
Table 13–11.Causes of pancytopenia. |Favorite Table|Download (.pdf) Table 13–11. Causes of pancytopenia.
Primary bone marrow disorders
Chronic idiopathic myelofibrosis
Infiltrative disease: lymphoma, myeloma, carcinoma, hairy cell leukemia, etc
Non–primary bone marrow disorders
Hypersplenism (with or without portal hypertension)
Systemic lupus erythematosus
Infection: tuberculosis, HIV, leishmaniasis, brucellosis, CMV, parvovirus B19
Nutritional deficiency (megaloblastic anemia)
Mild cases of aplastic anemia may be treated with supportive care, including erythropoietic (epoetin or darbepoetin) or myeloid (filgrastim or sargramostim) growth factors, or both. Red blood cell transfusions and platelet transfusions are given as necessary, and antibiotics are used to treat infections.
Severe aplastic anemia is defined by a neutrophil count of less than 500/mcL, platelets less than 20,000/mcL, reticulocytes less than 1%, and bone marrow cellularity less than 20%. The treatment of choice for young adults (under age 40 years) who have an HLA-matched sibling is allogeneic bone marrow transplantation. Children or young adults may also benefit from allogeneic bone marrow transplantation using an unrelated donor. Because of the increased risks associated with unrelated donor allogeneic bone marrow transplantation relative to sibling donors, this treatment is usually reserved for patients who have not responded to immunosuppressive therapy.
For adults over age 40 years or those without HLA-matched hematopoietic stem cell donors, the treatment of choice for severe aplastic anemia is immunosuppression with equine antithymocyte globulin (ATG) plus cyclosporine. Equine ATG is given in the hospital in conjunction with transfusion and antibiotic support. A proven regimen is equine ATG 40 mg/kg/day intravenously for 4 days in combination with cyclosporine, 6 mg/kg orally twice daily. Equine ATG is superior to rabbit ATG, resulting in a higher response rate and better survival. ATG should be used in combination with corticosteroids (prednisone or methylprednisolone 1–2 mg/kg/day orally for 1 week, followed by a taper over 2 weeks) to avoid ATG infusion reactions and serum sickness. Responses usually occur in 1–3 months and are usually only partial, but the blood counts rise high enough to give patients a safe and transfusion-free life. The full benefit of immunosuppression is generally assessed at 4 months post-equine ATG. Cyclosporine is maintained at full dose for 6 months and then stopped in responding patients. Androgens (such as fluoxymesterone 10–20 mg/day orally in divided doses) have been widely used in the past, with a low response rate, and may be considered in mild cases. Androgens appear to partially correct telomere length maintenance defects and increase the production of endogenous erythropoietin. The thrombopoietin mimetic, eltrombopag, may help increase platelets (and also red blood cells and white blood cells) in patients with refractory aplastic anemia.
Patients with severe aplastic anemia have a rapidly fatal illness if left untreated. Allogeneic bone marrow transplant from an HLA-matched sibling donor produces survival rates of over 80% in recipients under 20 years old and of about 65–70% in those 20 to 50 years old. Respective survival rates drop 10–15% when the donor is HLA-matched but unrelated. Equine ATG-cyclosporine immunosuppressive treatment leads to a response in approximately 70% of patients (including those with hepatitis virus–associated aplastic anemia). Up to one-third of patients will relapse with aplastic anemia after ATG-based therapy. Clonal hematologic disorders, such as PNH, AML, or myelodysplasia, may develop in one-quarter of patients treated with immunosuppressive therapy after 10 years of follow-up. Factors that predict response to ATG-cyclosporine therapy are patient’s age, reticulocyte count, lymphocyte count, and age-adjusted telomere length of leukocytes at the time of diagnosis.
All patients should be referred to a hematologist.
Admission is necessary for treatment of neutropenic infection, the administration of ATG, or allogeneic bone marrow transplantation.
A. Bone marrow transplantation for acquired severe aplastic anemia. Hematol Oncol Clin North Am. 2014 Dec;28(6):1145–55.
et al. Recent developments in drug therapy for aplastic anemia. Ann Pharmacother. 2014 Nov;48(11):1469–78.