Occult Blood, Fecal, IA

A screening test for the qualitative detection of fecal occult blood which may aid in the diagnosis of colorectal cancer, diverticulitis, colitis, polyps, and adenomas this test should be highly sensitive and highly specific for bleeding in the lower gastrointestinal tract, and providers should encourage patient compliance with obtaining a proper specimen. Guaiac-based tests for occult blood in stool suffer from a number of drawbacks, leading to a reduction in their sensitivity as well as production of false-positive results. These drawbacks include:

• Detection of heme present in the stool, which can originate from bleeding anywhere in the gastrointestinal tract

• Inability to distinguish human heme from heme present in many foods, such as dietary meats

• Indiscriminate detection of peroxidase activity, which is present in a wide range of fruits and vegetables

• Reaction with drugs and other substances that can cause false-negative results

Detection of fecal occult blood by immunoassay eliminates the drawbacks seen with guaiac-based tests, and provides a sensitivity and specificity that is superior to guaiac. Immunochemical fecal occult blood tests utilize antihuman hemoglobin antibodies to detect the globin portion of undegraded human hemoglobin in stool. While hemoglobin from the upper gastrointestinal tract is mostly degraded by bacterial and digestive enzymes before reaching the large intestine, hemoglobin from lower gastrointestinal tract bleeding undergoes less degradation and remains immunochemically reactive. Thus, these tests are specific for lower gastrointestinal tract bleeding. Additionally, immunochemical fecal occult blood tests do not react with animal hemoglobin; peroxidase compounds; or with drugs, vitamins, or other substances that can produce false results, thereby eliminating the need for dietary or drug restrictions prior to patient specimen collection.