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Medical Definition of Megalocytosis
1. The occurrence of unusually large numbers of macrocytes in the circulating blood. Synonym: macrocytosis, megalocythemia, megalocytosis. Origin: macrocyte + G. Haima, blood Hyperchromatic macrocythemia, an inexact term frequently used for macrocytes that contain an unusually large amount of haemoglobin, but are actually normochromic; although the total mass of haemoglobin is greater than normal (owing to the large cells), the percentage of haemoglobin in the cells is not greater than normal. (05 Mar 2000)