the search for disease, such as cancer, in people who do not have any symptoms. For example, screening tests for colon cancer include colonoscopy and the fecal occult blood test. Some of the same tests used for screening may also be used as diagnostic tests, which look for cancer in a person after there is some sign of a problem. For instance, a colonoscopy would be a diagnostic test if it was used in a person who had blood in the stool or symptoms of a blockage. See also colon, colonoscopy, fecal occult blood test.