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) primarily via elevated IL-6, 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, liver 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. The anemia is a consequence of (1) a relative resistance to red blood cell production in response to erythropoietin, (2) a decrease in erythropoietin production relative to the nephron mass, (3) a negative erythropoietic influence of higher levels of chronic inflammatory cytokines in older adults, and (4) the presence of various somatic mutations in myeloid genes typically associated with myeloid neoplasms. The latter condition is now referred to as clonal cytopenias of undetermined significance, which has a 1–1.5% per year rate of transformation to a myeloid neoplasm, such as a myelodysplastic syndrome. 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.