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Anisocytosis describes an abnormal variation in the size of red blood cells and is often found in iron deficiency anemia,
megaloblastic anemia, thalassemia, vitamin A or vitamin B 12 deficiency. Red cells varying in shape from elongated to oval, and rich in hemoglobin, are called elliptocytes/ovalocytes. They can be seen in hereditary disorders, such as hereditary elliptocytosis, or in acquired disorders, such as iron deficiency anemia, infectious anemias, thalassemia.