6: Anemia

Anemia can occur in isolation, or as a consequence of a process causing pancytopenia, the reduction of all 3 cell lines (white blood cells [WBCs], platelets, and red blood cells [RBCs]). This chapter focuses on the approach to isolated anemia, although a brief list of causes of pancytopenia appears in Figure 6-1. The first step in determining the cause of anemia is to identify the general mechanism of the anemia and organize the mechanisms using a pathophysiologic framework:

1. Acute blood loss: this is generally clinically obvious.

2. Underproduction of RBCs by the bone marrow; chronic blood loss is included in this category because it leads to iron deficiency, which ultimately results in underproduction.

3. Increased destruction of RBCs, called hemolysis.

Patients should always be assessed for signs and symptoms of acute blood loss.

1. Signs of acute blood loss

   1. Hypotension

   2. Tachycardia

   3. Large ecchymoses

2. Symptoms of acute blood loss

   1. Hematemesis

   2. Melena

   3. Rectal bleeding

   4. Hematuria

   5. Vaginal bleeding

   6. Hemoptysis

After excluding acute blood loss, the next pivotal step is to distinguish underproduction from hemolysis by checking the reticulocyte count:

1. Low or normal reticulocyte counts are seen in underproduction anemias.

2. High reticulocyte counts occur when the bone marrow is responding normally to blood loss; hemolysis; or replacement of iron, vitamin B₁₂, or folate.

3. Reticulocyte measures include:

   1. The reticulocyte count: the percentage of circulating RBCs that are reticulocytes (normally 0.5–1.5%).

   2. The absolute reticulocyte count; the number of reticulocytes actually circulating, normally 25,000–75,000/mcL (multiply the percentage of reticulocytes by the total number of RBCs).

   3. The reticulocyte production index (RPI)

      1. Corrects the reticulocyte count for the degree of anemia and for the prolonged peripheral maturation of reticulocytes that occurs in anemia.

         • (1) Normally, the first 3–3.5 days of reticulocyte maturation occurs in the bone marrow and the last 24 hours in the peripheral blood.

         • (2) When the bone marrow is stimulated, reticulocytes are released prematurely, leading to longer maturation times in the periphery, and larger numbers of reticulocytes present at any given time.

         • (3) For a HCT of 25%, the peripheral blood maturation time is 2 days, and for a HCT of 15%, it is 2.5 days; the value of 2 is generally used in the RPI calculation.

      2. 

      3. The normal RPI is about 1.0. In the setting of anemia, values < 2.0 indicate underproduction; those > 2.0 indicate hemolysis or an adequate bone marrow response to acute blood loss or replacement of iron or vitamins.

The first steps in evaluating anemia are looking for acute blood loss and checking the RPI in patients who are not acutely bleeding.

After determining the general mechanism, the next step in diagnosing the cause of anemia is to determine the cause of the underproduction or increased destruction. Traditionally, the differential diagnosis for underproduction anemia is framed using the cell size. While this is a useful way to organize the differential, and may at times provide useful clues, it is important to keep in mind that the mean corpuscular volume (MCV) is not specific and should not be used to rule in or rule out a specific cause of anemia.

Use the MCV to organize your thinking, not to diagnose the cause of an anemia.

1. Microcytic anemias (MCV < 80 mcm³)

   1. Iron deficiency

   2. Thalassemia

   3. Anemia of inflammation/chronic disease (more often normocytic)

   4. Sideroblastic anemia (congenital, lead exposure, medications)—rare

   5. Copper deficiency or zinc poisoning—rare

2. Macrocytic anemias (MCV > 100 mcm³)

   1. Megaloblastic anemias (due to abnormalities in DNA synthesis; hypersegmented neutrophils also occur)

      1. Vitamin B₁₂ deficiency

      2. Folate deficiency

      3. Antimetabolite drugs, such as methotrexate or zidovudine

   2. Nonmegaloblastic anemias (no hypersegmented neutrophils)

      1. Alcohol abuse

      2. Liver disease

      3. Hypothyroidism

      4. Myelodysplastic syndrome (often causes pancytopenia)

3. Normocytic anemias

   1. Anemia of inflammation/chronic disease (chronic kidney disease, infection, inflammation, malignancy, aging)

   2. Early iron deficiency

   3. Bone marrow suppression

      1. Invasion by malignancy or granulomas

      2. Acquired pure red cell aplasia (parvovirus B19, HIV, medications [mycophenolate mofetil, trimethoprim-sulfamethoxazole, phenytoin, recombinant human erythropoietins], thymoma, other malignancies, immune disorders)

      3. Aplastic anemia (often causes pancytopenia)

   4. Endocrine (hypopituitarism or hypothyroidism)

The framework for hemolytic anemias is pathophysiologic:

1. Hereditary

   1. Enzyme defects, such as pyruvate kinase or glucose-6-phosphate dehydrogenase (G6PD) deficiency

   2. Hemoglobinopathies, such as sickle cell anemia

   3. RBC membrane abnormalities, such as spherocytosis

2. Acquired

   1. Hypersplenism

   2. Immune

      1. Autoimmune: warm IgG, cold IgM, cold IgG

      2. Drug induced: autoimmune or hapten

   3. Mechanical

      1. Macroangiopathic (marching, prosthetic valves)

      2. Microangiopathic: disseminated intravascular coagulation (DIC), thrombotic thrombocytopenic purpura (TTP), and hemolytic uremic syndrome (HUS)

   4. Infections, such as malaria

   5. Toxins, such as snake venom and aniline dyes

Figure 6-1 outlines the approach to evaluating anemia, assuming acute bleeding has been excluded.

1. Symptoms in chronic anemia are due to decreased oxygen delivery to the tissues.

   1. Fatigue is a common but not very specific symptom.

   2. Dyspnea on exertion often occurs.

   3. Exertional chest pain occurs most often in patients with underlying coronary artery disease or severe anemia or both.

   4. Palpitations or tachycardia can occur.

   5. Edema is sometimes seen.

      1. It is due to decreased renal blood flow leading to neurohormonal activation and salt and water retention, similar to that seen in heart failure.

      2. However, in contrast to the low cardiac output seen in patients with heart failure, the cardiac output in patients with anemia is high.

   6. Mild anemia is often asymptomatic.

2. Symptoms of hypovolemia occur only in acute anemia caused by large volume blood loss.

3. Conjunctival rim pallor

   1. Present when the anterior rim of the inferior palpebral conjunctiva is the same pale pink color as the deeper posterior aspect, rather than the normal bright red color of the anterior rim.

   2. The presence of conjunctival rim pallor strongly suggests the patient is anemic (LR+ 16.7).

   3. However, the absence of pallor does not rule out anemia.

4. Palmar crease pallor has an LR+ of 7.9.

5. Pallor elsewhere (facial, nail bed) is not as useful, with LR+ < 5.

6. No physical sign rules out anemia.

7. The overall sensitivity and specificity of the physical exam for anemia is about 70%.

Order a CBC if patients have symptoms that suggest anemia, even without physical exam signs, or if you observe conjunctival rim or palmar crease pallor.

The first step is to determine the mechanism of Mrs. A's anemia. Mrs. A is not having any symptoms or signs of acute blood loss. She does have clinical findings suggestive of diseases associated with chronic blood loss: reflux possibly causing esophagitis and occasional menorrhagia. However, it is not possible to distinguish underproduction from hemolysis based on the history. Although the change in her CBC tells you a new process is going on, it also does not distinguish between these 2 mechanisms. The first pivotal point will be her reticulocyte count.

Always look at previous CBC results to see if the anemia is new, old, or progressive.

Mrs. A’s MCV is 76 mcm³, so you should consider the differential diagnosis for microcytic anemia. However, it is important to keep in mind that the MCV is not specific and should not be used to rule in or rule out a specific cause of anemia.

1. In one study, normal MCVs were found in 50% of patients with abnormal serum vitamin B₁₂, folate, or iron studies.

   1. 5% of patients with iron deficiency had high MCVs

   2. 12% of patients with vitamin B₁₂ or folate deficiency had low MCVs

2. What about the rest of the CBC? Do the other indices help?

   1. Other red cell indices (mean corpuscular hemoglobin [MCH] and mean corpuscular hemoglobin concentration [MCHC]) tend to trend with the MCV and are not particularly sensitive or specific.

   2. The red cell distribution width (RDW) is also not sensitive or specific in identifying the cause of an anemia.

Despite this caveat about the MCV, in a patient with a microcytic anemia and symptoms suggesting possible chronic blood loss, iron deficiency is by far the most likely cause, with a pretest probability of 80%. Therefore, the leading hypothesis for Mrs. A is iron deficiency anemia. Anemia of inflammation, by virtue of being common, is the best active alternative; to make this diagnosis, keep in mind that the patient must have an inflammatory condition known to cause anemia. Sideroblastic anemia and lead exposure are other hypotheses. Thalassemia is excluded by the recently normal CBC. Because the MCV lacks specificity, the causes of normocytic and macrocytic anemia also need to be kept in mind as other hypotheses. Table 6-1 lists the differential diagnosis.

Leading Hypothesis: Iron Deficiency Anemia

Textbook Presentation

The most classic presentation would be a young, menstruating woman who has fatigue and a craving for ice. Typical presentations include fatigue, dyspnea, and sometimes edema.

Disease Highlights

1. The CBC varies with the degree of severity of the iron deficiency.

   1. In very early iron deficiency, the CBC is normal, although the ferritin is already decreasing.

   2. A mild anemia then develops, with an Hgb of 9–12 g/dL, and normal or slightly hypochromic RBCs.

   3. As the iron deficiency progresses, the Hgb continues to decrease, and hypochromia and microcytosis develop.

2. Causes of iron deficiency

   1. Blood loss, most commonly menstrual or GI

   2. Inadequate intake

      1. Males need 1 mg/day (need to consume 15 mg/day; absorption rate 6%).

      2. Females need 1.4 mg/day (need to consume 11 mg/day; absorption rate 12%).

      3. Iron is more bioavailable from meat than vegetables.

   3. Malabsorption, seen in patients with gastrectomy, some bariatric surgery procedures, celiac sprue, or inflammatory bowel disease

   4. Increased demand, seen with pregnancy, infancy, adolescence, erythropoietin therapy

Evidence-Based Diagnosis

1. Bone marrow exam for absence of iron stores is the gold standard.

2. The serum ferritin is the best serum test.

   1. The LR+ for a decreased serum ferritin is very high, with reports ranging from LR+ of 51 for a ferritin < 15 ng/mL to a LR+ of 25.5 for a ferritin < 32 ng/mL.

   2. Thus, a low ferritin rules in iron deficiency anemia.

   3. In general populations, the LR– for a serum ferritin > 100 ng/mL is very low (0.08).

   4. Thus, in general populations, a ferritin > 100 ng/mL greatly reduces the probability the patient has iron deficiency.

   5. However, because ferritin is an acute phase reactant that increases in inflammatory states, interpreting it in the presence of such illnesses is difficult.

      1. There is a wide range of reported LRs, with many studies finding ferritin is not helpful in diagnosing iron deficiency in the presence of chronic illness.

      2. The level at which the serum ferritin suggests iron deficiency is probably much higher in patients with chronic illness, but the level may vary depending on the underlying illness.

      3. In chronic kidney disease, iron abnormalities are defined using the transferrin saturation (serum iron/total iron-binding capacity [Fe/TIBC]) and ferritin.

         • (1) Absolute iron deficiency, due to dietary deficiency, poor absorption, GI or other bleeding: transferrin saturation < 20%, ferritin < 100 ng/mL

         • (2) Functional iron deficiency, due to impaired iron transport to erythroblasts and inhibited intestinal absorption: transferrin saturation < 20%, ferritin ≥ 100 ng/mL

3. Other tests

   1. The MCV, the transferrin saturation, red cell protoporphyrin, red cell ferritin, and RDW all are less sensitive and specific than ferritin.

   2. The best of these is transferrin saturation ≤ 5%, with a LR+ of 10.46.

   3. The reticulocyte-hemoglobin, measured by automated blood counters, is low in 80% of cases of iron deficiency anemia and normal in more than 80% of cases of anemia of chronic inflammation. It is also low in thalassemia trait. The normal range is 28–38 pg.

In patients without chronic inflammatory diseases, the serum ferritin is the best single test to diagnose iron deficiency anemia.

Treatment

1. Iron deficiency anemia is generally treated with oral iron replacement, with IV iron therapy reserved for patients who demonstrate malabsorption or who are unable to tolerate oral iron.

2. Transfusion is necessary only if the patient is hypotensive, orthostatic, or actively bleeding; or has angina, dizziness, syncope, or severe dyspnea or fatigue.

3. The best-absorbed oral iron is ferrous sulfate; the dose is 325 mg 3 times daily.

4. There are significant GI side effects, including nausea, abdominal pain, and constipation; these can be reduced by taking the iron with food, and slowly titrating the dose from 1 tablet daily to 3 tablets daily over 1–2 weeks.

5. There should be an increase in reticulocytes 7–10 days after starting therapy, and an increase in Hgb and HCT by 30 days; if there is no response, reconsider the diagnosis, keeping in mind that adherence with iron therapy is often low.

6. It is necessary to take iron for 6 months in order to replete iron stores.

Since Mrs. A does not have any chronic, inflammatory diseases, the most useful test at this point is a serum ferritin. Serum iron and TIBC are often ordered simultaneously but are not necessary at this point.

Always look for a source of blood loss in iron deficiency anemia. Be alert for occult GI malignancies.

Iron deficiency is almost always due to chronic blood loss and rarely due to poor iron intake or malabsorption of iron; menstrual and GI blood loss are the most common sources. Because GI blood loss can be occult, many patients need GI evaluations.

1. Who needs a GI work-up? (also see Chapter 19, GI Bleeding)

   1. All men, all women without menorrhagia, and women over age 50 even with menorrhagia.

   2. Women under age 50 with menorrhagia do not need further GI evaluation, unless they have GI symptoms or a family history of early colon cancer or adenomatous polyps.

   3. Always ask carefully about minimal GI symptoms in young women, since celiac sprue often causes iron deficiency due to malabsorption, and the symptoms can easily be attributed to irritable bowel syndrome.

It is unclear from Mrs. A’s history whether the menorrhagia is sufficient to cause this degree of iron deficiency anemia. In addition, she has upper GI symptoms of anorexia and reflux. Therefore, you order an EGD, which shows severe reflux esophagitis and also gastritis. Further history reveals she has been using several hundred milligrams of ibuprofen daily for several weeks because of a back strain. The severe esophagitis and gastritis are sufficient to explain her anemia. Although she has no lower GI symptoms or family history of colorectal cancer, the American Gastroenterological Association recommends performing a colonoscopy.

Although Mrs. A is not anemic now, she has a marked macrocytosis. The approach to isolated macrocytosis is the same as the approach to macrocytic anemia. The degree of macrocytosis is not a reliable predictor of the cause, but in general, the higher the MCV, the more likely the patient has a vitamin B₁₂ or folate deficiency. The pretest probability of vitamin deficiency with an MCV of 115–129 mcm³ is 50%, and nearly all patients with an MCV > 130 mcm³ will have a vitamin deficiency.

B₁₂ deficiency is seen more often than folate deficiency in otherwise healthy people, and so is the leading hypothesis, with folate deficiency being the active alternative. Use of antimetabolite drugs is excluded by history. Causes of nonmegaloblastic anemias need to be considered next. Hypothyroidism would be the most likely other hypothesis, with liver disease and alcohol abuse less likely based on her lack of a previous history of either. Hemolysis causing reticulocytosis is unlikely since she is not anemic. Table 6-2 lists the differential diagnosis.

Leading Hypothesis: B12 Deficiency

Textbook Presentation

The classic presentation is an elderly woman with marked anemia and neurologic symptoms such as paresthesias, sensory loss (especially vibration and position), and ataxia.

Disease Highlights

1. It takes years to develop this deficiency because of extensive stores of vitamin B₁₂ in the liver.

2. Anemia and macrocytosis are not always present.

   1. In 1 study, 28% of patients with neurologic symptoms due to B₁₂ deficiency had no anemia or macrocytosis; another study found that up to 84% of patients with B₁₂ deficiency may be missed if B₁₂ levels are checked only in patients with macrocytosis.

   2. In another study, the following clinical characteristics were found in patients with B₁₂ deficiency:

      1. 33% white, 41% black, 25% Latino

      2. 28% were not anemic

      3. 17% had a normal MCV

      4. 17% had leukopenia, 35% thrombocytopenia, 12.5% pancytopenia

      5. 36% had neuropsychiatric symptoms

         • (1) Paresthesias occur initially, followed by ataxia with loss of vibration and position sense.

         • (2) Neuropsychiatric symptoms can progress to severe weakness, spasticity, clonus, paraplegia, fecal and urinary incontinence.

         • (3) Delirium and dementia can occur.

         • (4) The severity of the anemia is inversely correlated with the degree of neurologic dysfunction.

           The CBC can be normal in B₁₂ deficiency.

3. Intramedullary hemolysis can occur, leading to an increased lactate dehydrogenase (LD) and decreased haptoglobin.

4. B₁₂ absorption requires normal gastric and intestinal function.

   1. Dietary B₁₂ is protein bound and is released by acid peptic digestion in the stomach.

   2. Although intrinsic factor is made by the parietal cells of the gastric body and fundus, it does not bind to B₁₂ until both reach the jejunum.

   3. The B₁₂-intrinsic factor complex binds to receptors in the terminal ileum, where B₁₂ is absorbed.

5. The most common causes of B₁₂ deficiency are food cobalamin malabsorption, lack of intrinsic factor, and dietary deficiency; other causes of malabsorption are less common.

   1. Dietary deficiency is rare unless the patient follows a vegan diet.

   2. Food cobalamin malabsorption occurs when B₁₂ is not released from food proteins due to impaired acid peptic digestion.

      1. The B₁₂ deficiency in this condition is often subclinical and effects up to 20% of older adults.

      2. It is caused by atrophic gastritis and achlorhydria, which can be seen with chronic Helicobacter pylori infection, gastric surgery, and long-term use of acid suppressing drugs.

   3. Lack of intrinsic factor is caused by gastrectomy (all patients with total gastrectomy and 5% of patients with partial gastrectomy will become B₁₂ deficient) or pernicious anemia.

      1. Pernicious anemia is an immunologically mediated gastric atrophy leading to loss of parietal cells and a marked reduction in secretion of intrinsic factor.

      2. It is uncommon before age 30 and most often seen in patients over age 50, with a median age at diagnosis of 70–80 years.

      3. 25% of patients have a family history of pernicious anemia and 10% have autoimmune thyroid disease.

   4. B₁₂ deficiency can also be caused by malabsorption in the terminal ileum due to

      1. Ileal resection or bypass

      2. Tropical sprue

      3. Crohn disease

   5. Blind loop syndrome can cause B₁₂ deficiency due to utilization of B₁₂ by the bacteria.

   6. Sometimes drugs interfere with B₁₂ absorption, most notably metformin, colchicine, ethanol, and neomycin.

   7. Malabsorption may rarely be due to congenital disorders, such as transcobalamin II deficiency.

Evidence-Based Diagnosis

1. Determining whether a patient is B₁₂ deficient is more complicated than it seems.

   1. B₁₂ levels can be falsely low in folate deficiency, pregnancy, and oral contraceptive use.

   2. B₁₂ levels can be falsely normal in myeloproliferative disorders, liver disease, and bacterial overgrowth syndromes.

   3. The sensitivity of a B₁₂ level < 200 pg/mL for proven clinical B₁₂ deficiency is 65–95%; the specificity is 60–80%.

2. B₁₂ is a cofactor in the conversion of homocysteine to methionine, and of methmalonyl CoA (MMA) to succinyl CoA.

   1. Consequently, in B₁₂ deficiency, the levels of homocysteine and MMA increase.

   2. Therefore, another way to diagnosis B₁₂ deficiency is to measure homocysteine and MMA levels.

      1. In addition to B₁₂ deficiency, MMA can be elevated in chronic kidney disease and hypovolemia.

      2. Homocysteine can be elevated in folate or pyridoxine deficiency, chronic kidney disease, hypovolemia, and hypothyroidism.

      3. The sensitivity of MMA > 400 nmol/L for the diagnosis of B₁₂ deficiency is 98%; modest elevations in the 300–700 nmol/L range can be seen in chronic kidney disease. MMA > 1000 nmol/L is highly specific for B₁₂ deficiency.

      4. The sensitivity of homocysteine ranges from 85% to 96%; an elevated homocysteine is less specific than an elevated MMA.

3. Response to therapy is another way to establish the presence of B₁₂ deficiency.

   1. MMA and homocysteine normalize 7–14 days after the start of replacement therapy.

   2. The reticulocyte count increases in 7–10 days, and the hemoglobin increases in 30 days.

4. An algorithm for diagnosing B₁₂ deficiency in patients with macrocytic anemia

   1. B₁₂ level < 100 pg/mL: deficiency present

   2. B₁₂ level 100–350 pg/mL: check MMA and homocysteine levels

      1. If both normal, deficiency unlikely

      2. If both elevated, deficiency present

      3. If MMA alone elevated, deficiency present

      4. If homocysteine alone elevated, possible deficiency

   3. B₁₂ > 350 pg/mL: deficiency unlikely

      Very low or very high B₁₂ levels are usually diagnostic.

      Patients with neurologic symptoms consistent with B₁₂ deficiency should have MMA and homocysteine levels checked if the B₁₂ level is normal.

Treatment

1. IM cobalamin, 1000 mcg weekly for 6–8 weeks, and then monthly for life

2. Can also use oral cobalamin, 1000–2000 mcg daily

   1. Oral cobalamin is absorbed by a second, nonintrinsic factor dependent mechanism that is relatively inefficient.

   2. Compliance can be a problem.

   3. Patients with dietary deficiency and food cobalamin malabsorption can be treated with lower doses of oral B₁₂.

   4. Randomized trials have shown that oral and intramuscular replacement are equally effective, even in patients with pernicious anemia or gastrectomies.

3. Sublingual and intranasal formulations are available but have not been extensively studied.

Alternative Diagnosis: Folate Deficiency

Textbook Presentation

The classic presentation is an alcoholic patient with malnutrition and anemia.

Disease Highlights

1. Anemia and macrocytosis are the most common manifestations; neurologic symptoms do not occur.

2. Most often caused by inadequate intake (especially in alcoholic patients) or increased demand due to pregnancy, chronic hemolysis, leukemia.

3. Since absorption occurs in the jejunum, malabsorption is rare in the absence of short bowel syndrome or bacterial overgrowth syndromes.

4. Some drugs can cause folate deficiency, including methotrexate, phenytoin, sulfasalazine, and alcohol.

5. Along with B₁₂, folate is a cofactor for the conversion of homocysteine to methionine, so homocysteine levels increase in folate deficiency.

Evidence-Based Diagnosis

1. The sensitivity and specificity of serum folate measurements for the diagnosis of folate deficiency are not clear.

2. Levels can decrease within a few days of dietary folate restriction, or with alcohol use, even though tissue stores can be normal; levels increase with feeding.

3. RBC folate, which reflects folate status over the previous 3 months, correlates more strongly with megaloblastic changes than does serum folate; however, the sensitivity and specificity of RBC folate for the diagnosis of true deficiency are both low (about 70% each).

4. Elevated homocysteine is about 80% sensitive for the diagnosis of folate deficiency; the specificity is unknown.

5. A positive response to therapy is diagnostic.

6. A patient with a normal serum folate, normal RBC folate, and no response to folate replacement does not have folate deficiency.

Treatment

1. In patients with an acute deficiency, treat with 1 mg of folic acid daily for 1–4 months, or until there is complete hematologic recovery.

   1. Never treat folate deficiency without determining whether the patient is B₁₂ deficient.

   2. Folate replacement can correct hematologic abnormalities while worsening the neurologic symptoms specific to B₁₂ deficiency.

2. Patients with long-term increased demand, such as those with sickle cell anemia, should take 1 mg of folic acid daily indefinitely.

3. Women who are trying to conceive should take 800 mcg/day of a prenatal vitamin (contains 1 mg folic acid); pregnant women should take a prenatal vitamin.

Always check for B₁₂ deficiency in a patient with folate deficiency.

The next step is to determine the cause of the B₁₂ deficiency.

1. Test for pernicious anemia by sending anti-intrinsic factor and anti-parietal cell antibodies.

   1. Anti-intrinsic factor antibodies have a sensitivity of 50% and specificity of 100% for the diagnosis of pernicious anemia.

   2. Anti-parietal cell antibodies have a sensitivity of 80% and specificity of 50–100%.

2. Review history for other symptoms of malabsorption suggesting small bowel disease.

3. Assess for vegan diet

4. In older patients without other symptoms, negative antibodies, and adequate intake, consider food-cobalamin malabsorption.

It is not always possible to determine the site of malabsorption, and it is acceptable to treat such patients empirically with B₁₂ replacement.

The relatively acute drop in HCT is a pivotal point that suggests either bleeding or hemolysis; these are also the "must not miss" diagnoses. The usual causes of normocytic anemia need to be considered next. Anemia of inflammation/chronic disease is a common cause of normocytic anemia, with bone marrow infiltration and RBC aplasia being less common. You would also include causes of microcytic and macrocytic anemia in your list of other hypotheses. Anemia is common in elderly patients, occurring in 10% of community dwelling older adults. In one study of patients over 65 referred to a hematology clinic for evaluation of anemia, 25% had iron deficiency, 10% anemia of inflammation, 7.5% hematologic malignancies (including myelodysplastic syndrome), 4.6% thalassemia, 3.4% chronic kidney disease, and 5.7% miscellaneous causes (including hypothyroidism, B₁₂ deficiency, hemolysis, alcohol, medication). A specific cause could not be identified in 44% of the patients. However, since her anemia is acute, it is unlikely to be related solely to her age. Table 6-3 lists the differential diagnosis.

There are no symptoms or signs suggesting that she is having an active, acute episode of bleeding. The next step is to look for hemolysis and occult, subacute bleeding.

The low RPI points toward an underproduction anemia, not hemolysis. The elevated serum ferritin substantially reduces the likelihood that she is iron deficient, especially since she has no history of chronic inflammatory diseases. She does not have hypothyroidism, B₁₂ deficiency, or folate deficiency. She does not have pancytopenia, so bone marrow infiltration is unlikely.

Alternative Diagnosis: Anemia of Inflammation

Textbook Presentation

Because there is such a broad spectrum of underlying causes, there is no classic presentation of anemia of inflammation. It is most often discovered on a routine CBC that shows a normochromic, normocytic anemia, with a Hgb in the range of 8.5–9.5 g/dL.

Disease Highlights

1. Occurs in patients with acute or chronic immune activation

2. Cytokines (interferons, interleukins, tumor necrosis factor) induce changes in iron homeostasis.

   1. Dysregulation of iron homeostasis

      1. Increased uptake and retention of iron in reticuloendothelial system cells

      2. Limited availability of iron for erythropoiesis

   2. Impaired proliferation and differentiation of erythroid progenitor cells

   3. Blunted erythropoietin response

      1. Production of erythropoietin inadequate for degree of anemia

      2. Progenitor cells do not respond normally

   4. Increased erythrophagocytosis leads to decreased RBC half-life

3. Underlying causes of anemia of inflammation include

   1. Chronic kidney disease

      1. In patients with end-stage renal disease who undergo dialysis, the anemia is due to lack of erythropoietin and marked inflammation.

      2. In patients with lesser degrees of chronic kidney disease, the anemia is caused primarily by lack of erythropoietin and anti-proliferative effects of uremic toxins.

   2. Autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, vasculitis, sarcoidosis, and inflammatory bowel disease

   3. Acute infections caused by viruses, bacteria, fungi, or parasites

      1. Can occur within 24–48 hours in acute bacterial infections, with Hgb usually in the 10–12 g/dL range

      2. Occurs in as many as 90% of ICU patients, accompanied by inappropriately mild elevations of serum erythropoietin levels and blunted bone marrow response to endogenous erythropoietin

   4. Chronic infections caused by viruses, bacteria, fungi, or parasites

   5. Cancer, either hematologic or solid tumor

4. Noninflammatory chronic anemias also occur.

   1. Endocrinopathies, such as Addison disease, thyroid disease, panhypopituitarism can lead to mild chronic anemia.

   2. Liver disease can cause anemia.

Evidence-Based Diagnosis

1. There is no 1 test that proves or disproves a patient's anemia is from anemia of inflammation.

2. Instead, there are several diagnostic tests that can possibly be done, sometimes simultaneously and sometimes sequentially.

   An Hgb of < 8 g/dL suggests there is a second cause for the anemia, beyond the anemia of inflammation.

   1. Even in the presence of a disease known to cause anemia, it is important to rule out iron, B₁₂, and folate deficiencies.

   2. As discussed above, it can be difficult to interpret iron studies in the presence of inflammatory diseases; however, the typical pattern in anemia of inflammation is a low serum iron, low TIBC, normal percent saturation, and elevated serum ferritin.

   3. Erythropoietin levels will be low in chronic kidney disease and not appropriately elevated for the degree of anemia in inflammatory conditions; interpretation is difficult and measurement of the erythropoietin level is generally not useful diagnostically.

   4. C-reactive protein is often elevated in patients with anemia of inflammation.

   5. Pancytopenia suggests there is bone marrow infiltration or a disease that suppresses production of all cell lines.

      When you see pancytopenia, think about bone marrow infiltration, B₁₂ deficiency, viral infection, drug toxicity, hypersplenism, overwhelming infection, systemic lupus erythematosus, or acute alcohol intoxication.

   6. Bone marrow examination is necessary to establish the diagnosis when pancytopenia is present, serum tests are not diagnostic, the anemia progresses, or there is not an appropriate response to empiric therapy.

Treatment

1. Treat the underlying chronic disease, if possible.

2. Indications for erythropoietin therapy and appropriate target Hgb levels are evolving; iron should be given to all patients being treated with erythropoietin.

The leading hypothesis is hemolysis, with the pivotal point being the elevated reticulocyte count and RPI. Considering the normal ferritin and vitamin levels, the pretest probability of hemolysis is high. The only potential active alternative would be active bleeding, since an elevated reticulocyte count also occurs then; however, that would be clinically obvious. All other causes of anemia are alternative diagnoses to be considered only if the diagnosis of hemolysis is not supported by further testing. Table 6-4 lists the differential diagnosis.

Leading Hypothesis: Hemolysis

Textbook Presentation

The presentation of hemolysis depends on the cause. Patients can be asymptomatic or critically ill.

Disease Highlights

1. In macroangiopathic and microangiopathic hemolytic anemia and some complement-induced lysis, RBCs are destroyed in the intravascular space.

   1. Completely destroyed cells release free Hgb into the plasma, which then binds to haptoglobin, reducing the plasma haptoglobin level.

   2. Some Hgb is lysed intravascularly and then is filtered by the glomerulus, causing hemoglobinuria.

   3. Some filtered Hgb is taken up by renal tubular cells, stored as hemosiderin; hemosiderinuria occurs about a week later, when the tubular cells are sloughed into the urine.

   4. Damaged but incompletely hemolyzed cells are destroyed in the spleen.

2. Deformed RBCs and those coated with complement are usually destroyed in the extravascular space, in the liver or spleen.

   1. Most of the Hgb is degraded into biliverdin, iron, and carbon monoxide.

   2. Biliverdin is converted to unconjugated bilirubin and released into the plasma, increasing the unconjugated bilirubin level.

   3. Some free Hgb is released, which then binds to haptoglobin, again reducing the plasma haptoglobin level.

Evidence-Based Diagnosis

1. The reticulocyte count is usually at least 4–5%; in 1 study of autoimmune hemolytic anemia, the median was 9%.

2. The serum haptoglobin should be < 25 mg/dL.

   1. Sensitivity = 83%, specificity = 96% for hemolysis; LR+ = 21, LR– = 0.18

   2. Haptoglobin is an acute phase reactant.

3. The LD is often increased.

   1. Finding an increased LD and a decreased haptoglobin is 90% specific for the diagnosis of hemolysis.

   2. Finding a normal LD and a normal serum haptoglobin (> 25 mg/dL) is 92% sensitive for the absence of hemolysis.

4. The unconjugated bilirubin may be increased.

5. Plasma and urine Hgb should be elevated if the hemolysis is intravascular.

Treatment

Treatment depends on the underlying cause. In an autoimmune condition, immunosuppressive therapy, especially prednisone, is used. If hemolysis is associated with TTP and HUS, the treatment is plasmapheresis and immunosuppressive therapy.

The combination of the high pretest probability and the large LR+ for this level of haptoglobin confirms the diagnosis of hemolysis. Active bleeding has been ruled out by history and physical exam. At this point, any further testing should be aimed at determining the cause of the hemolysis.

1. The direct antiglobulin test (DAT), also known as the Coombs test, should be done in all patients to distinguish immune-mediated from non–immune-mediated hemolytic anemia.

   1. Detects antibody or complement on the surface of the RBC

      1. The DAT is positive for IgG in patients with warm autoimmune hemolytic anemia.

      2. The DAT is positive for complement in patients with cold autoimmune hemolytic anemia.

      3. It is also positive in paroxysmal cold hemoglobinuria, transfusion-related hemolytic anemia, and some drug-induced hemolytic anemias.

   2. The indirect Coombs test detects antibodies to RBC antigens in the patient's serum and is sometimes positive in drug-induced hemolytic anemias.

2. The smear should be examined for schistocytes, seen in macroangiopathic and microangiopathic hemolytic anemias.

   1. Concomitant thrombocytopenia and coagulopathy are seen in DIC.

   2. Concomitant thrombocytopenia, chronic kidney disease, or neurologic symptoms are seen in TTP and HUS.

3. Look for other causes of hemolytic anemia through history and physical exam and test selectively.

   1. Does the patient have a mechanical valve?

   2. Has the patient traveled to an area where malaria is endemic?

   3. Has the patient been exposed to a toxin?

   4. Does the patient have splenomegaly on exam or ultrasound?

   5. Is there an undiagnosed hereditary cause (especially G6PD deficiency)?

Sickle Cell Anemia

Textbook Presentation

Sickle cell anemia is often identified at birth through screening. Adult patients generally seek medical attention for pain or some of the complications (see below). Occasionally, patients have very mild disease, and sickle cell is diagnosed late in life when evidence of a specific complication, such as sickle cell retinopathy, is identified.

Disease Highlights

1. Epidemiology

   1. There are 5 haplotypes, 4 African and 1 Asian [Arab-Indian].

   2. Common genotypes include

      1. Sickle cell anemia (homozygous HbS gene)

      2. SC disease (HbS + HbC genes)

      3. HbS-beta-thalassemia (HbS + beta⁰ or beta⁺ thalassemia gene)

      4. HbSO Arabia (HbS + HbO Arabia genes)

      5. HbSD Los Angeles [Punjab] (HbS + HbD genes)

   3. In non-Hispanic white births, the gene frequency for sickle cell or thalassemia is 0.17%.

   4. In African Americans, the gene frequency of Hgb S is 4%, of Hgb C is 1.5%, and of beta-thalassemia is 4%; the incidence of sickle cell anemia is about 1 in 600, with the incidence of all sickle cell disease genotypes approaching 1 in 300.

2. Pathophysiology (Figure 6-2) of sickle cell disease

   1. Vaso-occlusion with ischemia-reperfusion injury

      1. Vascular obstruction is caused by precapillary obstruction by sickled cells and inflammatory triggers.

      2. Episodic microvascular occlusion and ischemia is followed by restoration of blood flow, leading to further injury during reperfusion as oxidases, cytokines, and other inflammatory mediators are activated.

   2. Hemolysis

      1. Contributes to progressive vasculopathy

      2. Patients with high hemolytic rates are more anemic and have more cholelithiasis, leg ulcerations, priapism, and pulmonary hypertension than patients with lower hemolytic rates.

      3. Patients with lower hemolytic rates tend to have more episodes of acute pain and possibly acute chest syndrome.

3. Prognosis

   1. Median age at death is 42 for men and 48 for women.

   2. Genetic factors can affect prognosis.

      1. Higher levels of fetal hemoglobin are associated with increased life expectancy, fewer acute pain episodes, and fewer leg ulcers; levels range from 1% to 30%.

      2. Coexistent alpha-thalassemia (30% of patients of African origin, 50% of patients of Arabian or Indian origin) leads to decreased rates of hemolysis and increased hemoglobin levels; pain frequency is not reduced, but the rates of stroke, gallstones, leg ulcers, and priapism are lower.

4. Sickle cell trait

   1. 8% of African Americans have sickle cell trait

   2. Patients with sickle cell trait are not anemic, do not have pain crises, and do not have increased mortality rates.

   3. Most cannot concentrate urine normally, but this is clinically important only if hydration is inadequate.

   4. Benign, self-limited hematuria due to papillary necrosis is common; however, renal medullary cancer, stones, glomerulonephritis, and infection should be ruled out.

   5. There is no need to routinely screen for sickle cell trait prior to surgery.

   6. Patients with sickle cell trait have a 2-fold increased risk for venous thromboembolism.

5. Clinical manifestations of sickle cell anemia

   1. Hematologic

      1. HCT usually 20–30%, with reticulocyte count of 3–15%; patients with HbSC disease and HbS-beta+-thalassemia tend to be less anemic.

      2. Hemoglobin levels decrease slightly during acute pain episodes and episodes of acute chest syndrome; acute, marked decreases can occur due to transient aplasia from parvovirus B19 infections or sudden sequestration by the liver or spleen.

      3. Unconjugated hyperbilirubinemia, elevated LD, and low haptoglobin are present.

      4. Hgb F level usually slightly elevated.

      5. WBC and platelet count usually elevated.

      6. Hypercoagulability occurs due to high levels of thrombin, low levels of protein C and S, abnormal activation of fibrinolysis and platelets

   2. Pulmonary

      1. Acute chest syndrome

         • (1) Defined as a new pulmonary infiltrate accompanied by fever and a combination of respiratory symptoms, including cough, tachypnea, and chest pain.

         • (2) Most common cause of death in sickle cell patients

         • (3) Clinical manifestations in adults shown in Table 6-5.

           • (a) About 50% of patients in whom acute chest syndrome develops are admitted for another reason.

           • (b) Over 80% have concomitant pain crises.

           • (c) Up to 13% require mechanical ventilation; 3% die.

         • (4) Etiology

           • (a) Fat embolism (from infarction of long bones), with or without infection in 12%

           • (b) Infection in 27%, with 8% due to bacteria, 5% mycoplasma, and 9% chlamydia

           • (c) Infarction in about 10%

           • (d) Hypoventilation and atelectasis due to pain and analgesia may play a role, as might fluid overload

           • (e) Unknown in about 50% of patients

         • (5) General principles of management

           • (a) Supplemental oxygen

           • (b) Empiric treatment with broad-spectrum antibiotics

           • (c) Incentive spirometry (can be preventive)

           • (d) Bronchodilators for patients with reactive airways

           • (e) Transfusion

      2. Sickle cell chronic lung disease

         • (1) 35–60% of patients with sickle cell disease have reactive airways.

         • (2) About 20% have restrictive lung disease, and another 20% have mixed obstructive/restrictive abnormalities.

         • (3) Up to 30% have pulmonary hypertension, with a very high risk of death compared to patients without pulmonary hypertension. Echocardiographic screening of adults every 1–3 years should be considered.

   3. Genitourinary

      1. Renal

         • (1) Inability to concentrate urine (hyposthenuria), with maximum urinary osmolality of 400–450 mOsm/kg

         • (2) Type 4 renal tubular acidosis

         • (3) Hematuria is usually secondary to papillary necrosis, but renal medullary carcinoma has been reported.

         • (4) Microalbuminuria is common in childhood, with up to 20% of adults developing nephrotic range proteinuria; ACE inhibitors reduce proteinuria.

         • (5) Chronic kidney disease develops in 30% of adults.

      2. Priapism

         • (1) 30–40% of adult males with sickle cell disease report at least 1 episode.

         • (2) Bimodal peak incidences in ages 5–13 and 21–29.

         • (3) 75% of episodes occur during sleep; the mean duration is 125 minutes.

         • (4) Treatment approaches include hydration, analgesia, transfusion, and injection of alpha-adrenergic drugs.

   4. Neurologic

      1. Highest incidence of first infarction is between the ages of 2 and 5, followed by another peak in incidence between the ages of 35 and 45.

      2. Hemorrhagic stroke can also occur.

      3. Recurrent infarction occurs in 67% of patients.

      4. Silent infarction is common (seen in 18–23% of patients by age 14); cognitive deficits also common.

      5. Patients over 2 years of age should undergo annual transcranial Doppler screening to assess stroke risk.

         • (1) Patients with elevated transcranial Doppler velocities (> 200 cm/s) are at high risk.

         • (2) Regular transfusions to keep the HbS level below 30% reduces the risk of stroke in such patients by 90% (10% stroke rate in control group, 1% in treatment group, number needed to treat (NNT) = 11).

   5. Musculoskeletal

      1. Bones and joints often the sites of vaso-occlusive episodes.

      2. Avascular necrosis of hips, shoulders, ankles, and spine can cause chronic pain.

         • (1) Often best detected by MRI

         • (2) May require joint replacement

   6. Other

      1. Retinopathy

         • (1) More common in patients with Hgb SC disease than with sickle cell (SS) disease

         • (2) Treated with photocoagulation

      2. Leg ulcers

         • (1) Present in about 20% of patients

         • (2) Most commonly over the medial or lateral malleoli

      3. Cholelithiasis: nearly universal due to chronic hemolysis

      4. Splenic sequestration and autosplenectomy: seen in children; leads to increased risk of infection with encapsulated organisms and the need for antibiotic prophylaxis

      5. Liver disease: multifactorial, due to causes such as iron overload or viral hepatitis

Evidence-Based Diagnosis

1. Newborn screening

   1. Universal screening identifies many more patients than screening targeted at high-risk groups.

   2. Homozygotes have an FS pattern on electrophoresis, which is predominantly Hgb F, with some Hgb S, and no Hgb A.

   3. The FS pattern in not specific for sickle cell disease, and the diagnosis should be confirmed through family studies, DNA based testing, or repeat Hgb electrophoresis at 3–4 months of age.

2. Testing in older children and adults

   1. Cellulose acetate electrophoresis separates Hgb S from other variants; however, S, G, and D all have the same electrophoretic mobility.

   2. Only Hgb S will precipitate in a solubility test such as the Sickledex.

Treatment

1. General principles

   1. All pediatric patients should receive prophylactic penicillin to prevent streptococcal sepsis.

   2. Indications for transfusion (preoperative transfusions and those for stroke prevention are evidence based; other indications are based on expert opinion or clinical practice)

      1. Acute transfusions: acute exacerbation of anemia, acute chest syndrome, acute stroke, multiorgan failure, preoperative management

      2. Chronic regular transfusions: primary and secondary stroke prevention, recurrent acute chest syndrome despite hydroxyurea therapy, progressive organ failure

      3. Patients should be monitored for iron overload and treated as needed.

   3. Hydroxyurea

      1. In patients with moderate to severe sickle cell disease, hydroxyurea therapy reduced the rate of pain crises and development of acute chest syndrome by about 50%.

      2. Hydroxyurea use is associated with a lower mortality rate.

   4. Stem cell transplant is an experimental therapy.

2. Management of vaso-occlusive crises

   1. The general approach should be similar to that used in patients with other causes of severe pain, such as cancer.

      1. Analgesics should be dosed regularly, rather than as needed.

      2. Patient-controlled analgesia can also be used.

      3. Remember that patients who use opioids long-term become tolerant and often require high doses for acute pain.

      4. Adding NSAIDs or tricyclic antidepressants to opioids is sometimes beneficial.

      5. Patients often need a long-acting opioid for baseline analgesia, combined with a short-acting opioid for breakthrough pain.

      6. A multidisciplinary approach to pain management involving nurses and social workers may help optimize pain management.

   2. Oral hydration is preferable to IV hydration.

   3. Oxygen is indicated only if the patient is hypoxemic.

Beta-Thalassemia

Textbook Presentation

Beta-thalassemia major (homozygotes) presents in infancy with multiple severe abnormalities. Heterozygotes are usually asymptomatic.

Disease Highlights

1. Impaired production of beta globin chains.

2. Common in patients of Mediterranean origin.

3. Beta-thalassemia minor: heterozygotes with 1 normal beta globin allele and 1 beta thalassemic allele.

4. Anemia is generally mild (HCT > 30%), and microcytosis is severe (MCV < 75 mcm³).

5. In pregnancy, anemia can be more severe than usual.

6. Splenomegaly is asymptomatic in 15–20% of patients.

Evidence-Based Diagnosis

1. Iron studies should be normal; RDW usually normal; target cells abundant; RBCs may be normal or high.

2. On Hgb electrophoresis, the Hgb A₂ can be elevated, but a normal A₂ does not rule out beta-thalassemia minor.

Treatment of Beta-Thalassemia Minor

None.

Alpha-Thalassemia

Textbook Presentation

Loss of 3 or 4 alpha globin genes causes severe disease that presents at birth or is fatal in utero. Patients with loss of 1 or 2 genes are usually asymptomatic.

Disease Highlights

1. Impaired production of alpha globin chains.

2. Common in patients of African or Asian origin.

3. Alpha-thalassemia-2 trait: loss of 1 alpha globin gene; CBC normal.

4. Alpha-thalassemia-1 trait (alpha-thalassemia minor): loss of 2 alpha globin genes; mild microcytic anemia with target cells and normal Hgb electrophoresis.

Evidence-Based Diagnosis

Alpha-thalassemia is diagnosed by polymerase chain reaction genetic analysis.

Treatment of Alpha-Thalassemia Trait

None.