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Elliptocytes in a patient with hereditary elliptocytosis. Elliptocytes are elongated oval-shaped red blood cells. Very rare elliptocytes may be seen in normal blood smears. Elliptocytes may be increased in iron deficiency anemia (where they are sometimes referred to as “pencil cells”) and marrow infiltrative processes (with teardrop cells). In hereditary elliptocytosis, caused by a red cell membrane structural defect, at least 25% of red cells are elliptocytes. The terms “elliptocyte” and “ovalocyte” are sometimes used interchangeably.