What are the specific causes of occult bleeding that may lead to iron deficiency anemia?
Common teaching used to be that iron deficiency anemia was usually caused by colon cancer, especially lesions in the right colon, because their bleeding can remain undetected for long periods of time. However, many studies have now documented that occult bleeding can occur as a result of a lesion (or lesions) from virtually anywhere in the gastrointestinal tract (and even from the oral cavity or nasopharyngeal area) (Table 1). Indeed, iron deficiency anemia is not uncommonly caused by an abnormality found in the upper gastrointestinal tract. Particularly common are severe ulcerative processes in the upper gastrointestinal tract (esophageal/gastric/duodenal ulcer). A number of other lesions can bleed chronically and also cause iron deficiency anemia. The most common cause of iron deficiency anemia worldwide is probably hookworm, (see http://www.cdc.gov/NCIDOD/dpd/parasites/hookworm/factsht_hookworm.htm) because these small parasites are capable of removing significant amounts of blood f
