Fecal Occult Blood Test

The fecal occult blood test detects hidden blood in the stool that is not visibly apparent, distinguishing it from conditions where bleeding is obvious. The traditional guaiac test smears a stool sample onto chemically treated paper, which changes color when hydrogen peroxide is applied if blood is present, but modern medicine increasingly favors the fecal immunochemical test, which uses antibodies to detect globin directly and is now recommended over the older guaiac method by the American College of Gastroenterology. Used as a colorectal cancer screening tool, roughly 1 to 5 percent of a large screened population test positive, of whom 2 to 10 percent are found to have cancer and 20 to 30 percent have precancerous polyps, though colonoscopy remains the preferred screening method for people at average risk beginning at age fifty.