CLINICAL GUIDELINE: PART II: Screening for Colorectal Cancer with the Fecal Occult Blood Test: A Background Paper

Purpose: Screening for colorectal cancer with fecal occult blood tests or sigmoidoscopy can reduce mortality rates. If occult blood testing is done, clinicians must decide how to interpret the results and plan further management. If the results are positive, a decision must be made about evaluating the colon. This report provides information that can be used to perform fecal occult blood tests, interpret the results of those tests, and plan patient management. Data Sources: The MEDLINE database was searched for data relevant to optimizing the technique of fecal occult blood testing. Studies were also identified from the bibliographies of published articles about test performance and the interpretation of test results, particularly sensitivity, specificity, and the probability of colorectal cancer after a positive test result. Study Selection and Data Extraction: Studies were selected and data were extracted on the basis of the authors' combined judgment. Data Synthesis: When used for screening, fecal occult blood tests have positive results about 1% to 16% of the time, depending on such factors as the age of the person being tested, whether the sample is rehydrated, and whether the test is used for initial screening or for rescreening. When the colons of persons who have positive test results are evaluated, the rate of finding any colorectal cancer is about 2% to 17% and the rate for early colorectal cancer (Dukes stage A or B) is about 2% to 14%. Conclusions: These results suggest that, in general, persons who have positive results on a fecal occult blood test should have a full colonic examination. More research is needed to understand and improve the sensitivity and specificity of the fecal occult blood test.