The CBC shows a pancytopenia (low white count, low red count, and low platelet count), although the platelet count may be only borderline low (see normal values on the front cover of this textbook). Pancytopenia in the CBC combined with macrocytosis should raise the index of suspicion toward a megaloblastic process because few other conditions (aplastic anemia, hyper-splenism) show this pattern.4 Red cell inclusions such as basophilic stippling and Howell-Jolly bodies may be observed. Howell-Jolly bodies formed from mega-loblastic erythropoiesis are larger and more fragmented in appearance than normal Howell-Jolly bodies. There is a low reticulocyte count (less than 1%) and the RDW is increased, owing to schistocytes, targets, and teardrop cells. The blood smear in megaloblastic anemia is extremely relevant in the diagnosis and shows macrocytes, macro-ovalocytes, hypersegmented multi-lobed neutrophils, and little polychromasia with respect to the anemia (Fig. 6.4). The presence of hyper-
segmented neutrophils (lobe count of more than five lobes) in combination with macrocytic anemia is a morphological marker for megaloblastic anemias. This qualitative white cell abnormality appears early in the disease and survives through treatment. It is usually the last morphology to disappear. The MCV initially is extremely high and may be in the range of 100 to 140 fL. A bone marrow examination is not necessary for the diagnosis of megaloblastic anemia, because the diagnosis of this disorder can be adequately made without this time-consuming, costly, and invasive procedure.
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