<Li> In the United States, the most common cause of iron deficiency is bleeding or blood loss, usually from the gastrointestinal tract . Fecal occult blood testing, upper endoscopy and lower endoscopy should be performed to identify bleeding lesions . In older men and women, the chances are higher that bleeding from the gastrointestinal tract could be due to colon polyps or colorectal cancer . </Li> <Li> Worldwide, the most common cause of iron deficiency anemia is parasitic infestation (hookworms, amebiasis, schistosomiasis and whipworms). </Li> <P> The Mentzer index (mean cell volume divided by the RBC count) predicts whether microcytic anemia may be due to iron deficiency or thallasemia, although it requires confirmation . </P> <Ul> <Li> Megaloblastic anemia, the most common cause of macrocytic anemia, is due to a deficiency of either vitamin B, folic acid, or both . Deficiency in folate or vitamin B can be due either to inadequate intake or insufficient absorption . Folate deficiency normally does not produce neurological symptoms, while B deficiency does . <Ul> <Li> Pernicious anemia is caused by a lack of intrinsic factor, which is required to absorb vitamin B from food . A lack of intrinsic factor may arise from an autoimmune condition targeting the parietal cells (atrophic gastritis) that produce intrinsic factor or against intrinsic factor itself . These lead to poor absorption of vitamin B . </Li> <Li> Macrocytic anemia can also be caused by removal of the functional portion of the stomach, such as during gastric bypass surgery, leading to reduced vitamin B / folate absorption . Therefore, one must always be aware of anemia following this procedure . </Li> </Ul> </Li> <Li> Hypothyroidism </Li> <Li> Alcoholism commonly causes a macrocytosis, although not specifically anemia . Other types of liver disease can also cause macrocytosis . </Li> <Li> Drugs such as methotrexate, zidovudine, and other substances may inhibit DNA replication such as heavy metals </Li> </Ul>

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