Screening Tests
Screening tests include stool tests that detect occult fecal blood, such as fecal immunochemical tests, high-sensitivity guaiac-based tests, and tests that detect abnormal DNA. Endoscopic tests are also used for screening, including colonoscopy, which visualizes the entire colon and can remove polyps, and flexible sigmoidoscopy, which visualizes the distal 60 cm of the bowel. Imaging tests include the double-contrast barium enema and CT colonography. Any abnormal finding on a stool test, imaging study, or flexible sigmoidoscopy warrants further evaluation with colonoscopy. Screening programs using fecal blood testing or flexible sigmoidoscopy have been shown in randomized trials to reduce the risk colorectal cancer death by about 15% to 30%. Although colonoscopy is the gold standard diagnostic test for screening, there is no direct evidence from randomized trials that screening with colonoscopy reduces colorectal cancer incidence or mortality. Complications of colonoscopy include perforation and bleeding; patients are usually sedated during the procedure, but many are averse to the extensive bowel preparation required.
Guidelines
The USPSTF and a collaborative multiorganizational group, consisting of the American Cancer Society, the U.S. Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology, both strongly endorse colorectal cancer screening and have issued screening guidelines. The USPSTF, which gives a grade A recommendation for colorectal cancer screening in average-risk adults ages 50 to 75 years, suggests several screening options, and advises that routine screening stop at age 75 years (see below). The multiorganizational group additionally recommends using double-contrast barium enema or CT colonography every 5 years as well as the fecal DNA test. However, there is no evidence that screening with these tests will reduce colorectal cancer incidence or mortality. Performing digital rectal examination is not recommended for colorectal cancer screening.
Although screening reduces colorectal cancer incidence and mortality, only about two thirds of the adult U.S. population has complied with recommended screening guidelines, and over a quarter has never been screened. Colonoscopy is the most commonly used test, though people may prefer other tests like FOBTs because they are safer and easier to perform. Keep in mind that the best screening test is the one that gets done! Higher-risk persons, based on personal history of colorectal neoplasia or longstanding inflammatory bowel disease, or a family history of colorectal neoplasia, should begin screening at a younger age, usually with colonoscopy, and get more frequent testing than average-risk adults.
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