How do the results of chemical fecal occult blood testing compare with immunologic fecal occult blood testing?
A chemical fecal occult blood test is inexpensive and easy, but it has several disadvantages. • Substances in fruits and vegetables can mimic heme and cause chemical fecal occult blood tests to be falsely positive, that is, falsely abnormal. Therefore, it is necessary to restrict certain fruits and vegetables before and during the collection of stool samples. • Unlike heme which can travel intact from the stomach or small intestine and into the stool, globin is destroyed in the small intestine. As a result, a positive chemical fecal occult blood test can be caused by bleeding anywhere in the stomach or intestines, but a positive immunologic fecal occult blood test only occurs when there is bleeding into the colon. Therefore, it is necessary to restrict red meat containing hemoglobin before and during the collection of stool samples or the heme from the ingested meat will cause a falsely positive test. • Some drugs commonly cause small amounts of bleeding into the stomach or small intes
