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Am Fam Physician. 2006;73(10):1707-1708

Screening for colon cancer affords family physicians an opportunity to affect the health of their patients. High-quality evidence has proved that screening saves lives,1,2 and colon cancer screening falls well within accepted cost-effectiveness parameters.3 Furthermore, a menu of screening options enables nearly every person to find an affordable, acceptable test.4,5 Public health efforts are increasing awareness of the benefits of screening,6 yet screening rates remain frustratingly low.7 Moreover, many physicians use a “screening test” that is not included in any guideline: a fecal occult blood test (FOBT) obtained at the time of a digital rectal examination (DRE).8

Physicians cite compelling arguments to justify the use of FOBT at the time of DRE. The central argument is that the patient in the office constitutes a captive audience. Performing the FOBT while the patient is in the office guarantees a 100 percent return rate. Some physicians have been able to generate a reimbursable charge for FOBT, even though the office test does not meet Medicare criteria. Furthermore, definitive evidence demonstrating the inadequacy of the DRE approach has been lacking until recently.

A study by Collins and colleagues9 in the Veteran's Affairs Cooperative Study Group should put an end to performing FOBT with DRE. They studied 2,665 persons between 50 and 75 years of age who were at average risk of colon cancer. Each person underwent three examinations: FOBT performed at home on three spontaneously passed stool specimens with the Hemoccult II test; FOBT following DRE in the physician's office; and colonoscopy, which was used to establish the sensitivity, specificity, and predictive value of the two FOBT procedures. This was the first prospective study specifically designed to assess the performance characteristics of the two approaches to FOBT, and the results were definitive. Home FOBT results were positive in 23.9 percent of persons who were found to have an adenomatous polyp of at least 1 cm, a villous adenoma, a dysplastic polyp, or cancer. FOBT obtained by DRE yielded positive results in only 4.9 percent of these patients. A negative FOBT result on DRE offered virtually no reassurance; patients with negative results on office testing had essentially the same likelihood of having advanced neoplasia as persons who underwent no stool testing at all.

Although the question of the reliability of DRE needed to be answered, the outcome does not make screening any easier. At-home FOBT is far from a perfect test. The 23.9 percent sensitivity of the six-window test is relatively low and reinforces the importance of repeating the test annually. Of concern, 12 of 21 patients with cancer tested negative on at-home FOBT. The other screening options have other obstacles to successful widespread completion.10 Fecal immunochemical testing is likely to gradually replace guaiac-based testing as the preferred technology for stool testing. The performance characteristics of this test, including the patient return rate, are superior to guaiac-based strategies.5

If you are relying on DRE to screen for colon cancer, you must stop. Instead, recommend one or more of the screening tests listed in virtually every guideline. Giving your patients the opportunity to choose from a menu of screening options increases the likelihood that each patient will find a test that he or she will adhere to. As for all aspects of preventive care, developing office systems that involve the entire office staff and that use paper or electronic prompts and tracking devices significantly increases the probability of reaching all of your eligible patients.

When age-eligible patients are seeing you for reasons other than colorectal cancer screening, take the opportunity to recommend one of the proven screening options. Scheduling specific preventive care visits is a particularly effective strategy to increase screening rates.11 No matter which approach is used—opportunistic screening or screening at a preventive visit—make sure that you follow one of several recommended screening guidelines: at-home FOBT every year, flexible sigmoidoscopy every five years (with or without annual FOBT), double-contrast barium enema every five years, or colonoscopy every 10 years.

DRE may be an easy way out, but the reassurance it offers you and your patients is false. Screen for colorectal cancer the right way: skip DRE and use tests that are proven to work.

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