hematology and oncology
Megaloblastic Macrocytic Anemias
Introduction
Megaloblastic anemias result most often from deficiencies of vitamin B12 and folate. Ineffective hematopoiesis affects all cell lines but particularly red blood cells. Diagnosis is usually based on a complete blood count and peripheral smear, which usually shows a macrocytic anemia with anisocytosis and poikilocytosis, large oval red blood cells (macro-ovalocytes), Howell-Jolly bodies (residual fragments of the nucleus), hypersegmented neutrophils, and reticulocytopenia. Treatment is directed at the underlying disorder. (See also Overview of Decreased Erythropoiesis .) Megaloblasts are large nucleated red blood cell (RBC) precursors with noncondensed chromatin due to impaired DNA synthesis. Macrocytes are enlarged RBCs (ie, mean corpuscular volume [MCV]>100 fL). Macrocytic RBCs occur in a variety of clinical circumstances, many unrelated to megaloblastic maturation. 