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Megaloblastic anemia is an anemia (of macrocytic classification) which results from inhibition of DNA synthesis in red blood cell production. It is often due to deficiency of vitamin B12 and/or folic acid. It can be the result of a lack of intrinsic factor (which lack interferes with B12 absorption), causing pernicious anemia, or with other antimetabolites which poison DNA production, such as chemotherapeutic agents.
It is characterized by many large immature and dysfunctional red blood cells (megaloblasts) in the bone marrow, and also by hypersegmented or multisegmented neutrophils.
The blood film can point towards vitamin deficiency:
The Schilling test was performed in the past to determine the nature of the vitamin B12 deficiency, but due to the lack of available radioactive B12, it is now largely a historical artifact. Vitamin B12 is a necessary prosthetic group to the enzyme methylmalonyl-coenzyme A mutase. B12 deficiency leads to dysfunction of this enzyme and a buildup of its substrate, methylmalonic acid, the elevated level of which can be detected in the urine and blood. Since the level of methylmalonic acid is not elevated in folic acid deficiency, this test provides a one tool in differentiating the two. However, since the test for elevated methylmalonic acid is not specific enough, the gold standard for the diagnosis of B12 deficiency is a low blood level of B12. Unlike the Shilling test, which often included B12 with intrinsic factor, a low level of blood B12 gives no clue as to the etiology of the low B12, which can from several causes.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Megaloblastic_anemia". A list of authors is available in Wikipedia.|