Megaloblastic anemia

Megaloblastic anemia is a form of macrocytic anemia in which red blood cells are too large and the bone marrow holds many large, immature cells called megaloblasts. It results from impaired DNA synthesis during red cell production, which lets the cells keep growing without dividing. The cause is most often a deficiency of vitamin B12 or folate, for example from pernicious anemia, a vegan diet without supplements, celiac disease, alcoholism or pregnancy, though drugs such as azathioprine and trimethoprim, and some inherited disorders of DNA synthesis, can also cause it. Onset is slow compared with other anemias, and a blood smear typically shows hypersegmented neutrophils. Treatment follows the cause, usually replacing the missing vitamin.