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Three-quarters of doctors use the wrong screening test for colorectal cancer, the CDC says [Updated]

May 10, 2010 |  3:52 pm

Three-quarters of physicians who use a fecal occult blood test to screen for colorectal cancer use an office test rather than the more sensitive home test, Centers for Disease Control and Prevention researchers reported Monday. Using the office test contradicts national guidelines for the procedure, which were developed because the test misses 95% of tumors and problematic polyps. The in-office test "may be worse than no screening at all" because it gives many patients a false sense of security, said epidemiologist Marion Nadel of the CDC's Division of Cancer Prevention and Control, who led the study.

[Updated May 11: The standard home test misses 76% of potential tumors, but the sensitivity is increased by performing the test every year. Newer tests have a higher sensitivity.]

The tests rely on the fact that many colorectal cancers bleed into the intestines. Although this blood is not readily visible in feces -- it is hidden or occult -- it can be detected with a variety of tests. The in-office test relies on the physician to perform a rectal examination, removing a small amount of feces for the test. The at-home test, in contrast, uses a regular bowel movement, which is much more likely to contain blood if any is present.

Nadel and her colleagues studied 1,134 primary care physicians who reported using such tests at least once a month. They reported in the current issue of the Journal of General Internal Medicine that a quarter said they used in-office tests exclusively, while an additional 53% reported using both in-office and home tests. Moreover, 60% of them used the least sensitive tests, which use the chemical guaiac to detect blood. The good news was that when a positive test was obtained, 93% of the physicians ordered a colonoscopy as a follow-up. That is the recommendation of national guidelines.

Among those who used the at-home tests, moreover, only 44% of physicians said they had a reminder system to encourage patients to complete the tests.

"Many primary care physicians continue to use inappropriate [fecal occult blood test] methods to screen for colorectal cancer, thereby missing the opportunity to save lives," Nadel said in a statement. The test "is an important option for screening, but it must be implemented correctly."

-- Thomas H. Maugh II