Occult Blood, Fecal, Immunoassay Test
An occult blood, fecal, immunoassay test is the qualitative detection of fecal occult blood.
A screening test for colorectal cancer, diverticulitis, colitis, polyps, and adenomas should be highly sensitive and highly specific for bleeding in the lower gastrointestinal tract and 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 and the 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 superior to guaiac. Immunochemical fecal occult blood tests utilize antihuman hemoglobin antibodies to detect the globin portion of undegraded human hemoglobin in stool. While bacterial and digestive enzymes mostly degrade hemoglobin from the upper gastrointestinal tract 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 before patient specimen collection.
The Polymedco OC-Auto Micro 80 immunochemical fecal occult blood test is capable of detecting as little as 100 ng of human hemoglobin per mL of feces, making it a much more sensitive assay than guaiac-based tests for detecting low levels of human fecal occult blood. It requires only one stool specimen collected from one bowel movement.
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