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| ==Overview== | | ==Overview== |
| ==Classification== | | ==Classification== |
| ===Megaloblastic anemias (DNA replication disorders)===
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| * Commonest cause of macrocytic anemia.
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| * In [[megaloblastic anemia]]s cells are larger because they cannot produce DNA quickly enough to divide at the right time as they grow, and thus grow too large before division.
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| * Causes for the DNA synthetic problem range from lack of certain vitamins needed to produce DNA (notably [[folate]] and [[B12]]), to poisons or inhibitors of DNA replication, such as some kinds of antiviral drugs and chemotherapeutic agents.
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| * The pathognomonic findings of megaloblastic anemia are: megaloblasts in [[bone marrow]], ovalocytes in the (peripheral) blood smear, and hypersegmented [[neutrophils]].
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| ===Non megaloblastic macrocytic anemias===
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| * Non megaloblastic macrocytic anemias, are disorders associated with increased red cell membrane surface area
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| * It is commonly associated with pathologies of the liver and spleen which produce [[codocyte]]s or "target cells" which have a central collection of hemoglobin surrounded by a pallor (a thin area) then followed by a thicker collection of hemoglobin at the rim of the cell.
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| ===Alcohol===
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| * Round macrocytes which are not codocytes are produced in chronic alcoholism (which produces a mild macrocytosis even in the absence of vitamin deficiency), apparently as a direct toxic effect of alcohol specifically on the bone marrow.
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| ===Association with rapid red cell turnover and reticulocytosis===
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| Mild macrocytocis is a common finding associated with rapid blood restoration or production, since in general, "fresh" or newly-produced red cells ([[reticulocytes]]) are larger than the mean (average) size, due to slow shrinkage of normal cells over a normal red cell circulating lifetime. Thus, [[chronic obstructive pulmonary disease]] (COPD), in which which red cells are rapidly produced in response to low oxygen levels in the blood, often produces mild macrocytosis. Also, rapid blood replacement from the marrow after a traumatic blood loss, or rapid red blood cell turnover from rapid hemolysis, also often produces mild macrocytosis in the associated anemia.
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| ==References== | | ==References== |