An anemic patient has the following red cell indexes: mean corpuscular volume, 70 mm3 ; mean corpuscular hemoglobin, 22 pg; and mean corpuscular hemoglobin concentration, 34%. These values are most consistent with a diagnosis of
The differential diagnosis of microcytosis includes b thalassemia (due to a defect in globin chain synthesis) and iron-deficiency anemia. It is impoant to distinguish between these two disorders because therapy with iron benefits patients with iron-deficiency anemia, but harms patients with thalassemia because these patients are at risk for iron overload. Both thalassemia minor and iron-deficiency anemia are microcytic disorders in which the mean corpuscular hemoglobin is usually found to be reduced. Red blood cell indexes may be useful in differentiating the two disorders because, while the mean corpuscular hemoglobin concentration (MCHC) is often normal or only slightly reduced in association with thalassemia minor, the MCHC is often definitely reduced in association with iron-deficiency anemia. (Both pernicious and folate-deficiency anemias lead to megaloblastic changes in erythrocytes.) The red cell distribution width (RDW) is a measure of variation in the size of the red cells (anisocytosis). The RDW is increased in patients with iron-deficiency anemia, but is normal in patients with b thalassemia. Also unique to the microcytic anemias is the fact that patients with b thalassemia have increased red blood cell counts, while patients with all of the other microcytic anemias have decreased red blood cell counts. This increased red cell count in b thalassemia may be due to the increased hemoglobin F, which shifts the oxygen dissociation curve to the left. This in turn causes an increased release of erythropoietin. Unlike iron-deficiency anemia, b thalassemia begins as a microcytic anemia. In contrast, irondeficiency anemia progresses through several stages. First there is decreased storage iron, which is followed by decreased circulating iron. At this time patients are still not clinically anemic. Next patients develop a normocytic normochromic anemia that transforms into a microcytic normochromic anemia and finally a microcytic hypochromic anemia. Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition.
Folic acid-deficiency anemia
Iron-deficiency anemia
Pernicious anemia
Thalassemia minor
miscellaneous