An important type of anaemia caused by a deficiency of vitamin B12 or another vitamin, folic acid. Either of these deficiencies seriously interferes with production of red blood cells in the bone marrow. An excess of cells called megaloblasts appears in the marrow. Megaloblasts give rise to enlarged and deformed red blood cells known as macrocytes.
Vitamin B12 is found only in foods of animal origin, such as meat and dairy products. It is absorbed from the small intestine after first combining with intrinsic factor, a chemical produced by the stomach lining. The most common cause of vitamin B12 deficiency is failure of the stomach lining to produce intrinsic factor, usually due to an autoimmune disorder; this is called pernicious anaemia. Total gastrectomy (removal of the stomach) prevents production of intrinsic factor, and removal of part of the small intestine prevents B12 absorption, as does the intestinal disorder Crohn’s disease. In a minority of cases, vitamin B12 deficiency is due to a vegan diet.
Folic acid is found mainly in green vegetables and liver. The usual cause of deficiency is a poor diet. Deficiency can also be caused by anything that interferes with the absorption of folic acid from the small intestine (for example Crohn’s disease or coeliac disease). Folic acid requirements are greater than normal in pregnancy.
Many people with mild megaloblastic anaemia have no symptoms. Others may experience tiredness, headaches, a sore mouth and tongue, and mild jaundice. If B12 deficiency continues for a long time, additional symptoms due to nerve damage, including numbness and tingling in the feet, may develop.
Megaloblastic anaemia is diagnosed by blood tests and a bone marrow biopsy. Megaloblastic anaemia due to poor diet can be remedied with a short course of vitamin B12 injections or folic acid tablets and the introduction of a normal diet. A lifelong course of vitamin B12 injections or folic acid tablets is required if the underlying cause of malabsorption is untreatable.... anaemia, megaloblastic
n. an abnormal form of any of the cells that are precursors of red blood cells (see erythroblast). Megaloblasts are unusually large and their nuclei fail to mature in the normal way; they are seen in the bone marrow in certain anaemias (megaloblastic anaemias) due to deficiency of vitamin B12 or folate. —megaloblastic adj.... megaloblast
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