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Data: Colon test did not find growth

Patrick Walters Associated Press

PHILADELPHIA – A common screening test failed to detect potentially cancerous colon growths 95 percent of the time, falsely reassuring patients and doctors, a new study found.

Researchers found that the digital in-office test on stool samples was not as reliable as a six-sample test given to patients to do at home – although even that test detected potentially cancerous growths less than 24 percent of the time.

“What we found is that it was pretty worthless,” Dr. David Lieberman, one of the study’s authors, said of the in-office test. “It’s a wake-up call that we shouldn’t be relying on this test.”

The study, published today in Annals of Internal Medicine, was conducted at 13 Veterans Affairs medical centers and involved 2,665 patients – most of them men – who were given the at-home test and the in-office test followed by a colonoscopy. The digital fecal occult blood test was positive in only 5 percent of patients with tumors or large precancerous growths called polyps; the take-home test found 24 percent.

The reliability of the at-home test, however, improves if patients use it every year, said Lieberman, gastroenterogy chief at Portland VA Medical Center in Oregon.

Because polyps and tumors often bleed intermittently, the chances of detecting them increase as more samples are taken over time, he said.

Early testing can find growths before they turn cancerous, a process that can take five to seven years, Lieberman said. The take-home test was positive for 43 percent of patients who actually had cancer, the study said.

A survey of physicians also published in Annals of Internal Medicine found that about a third used only the office test, a fourth used only the home test, and about 40 percent used both.

The survey was funded by the National Cancer Institute and the Centers for Disease Control and Prevention, said one possible reason for using the office tests was concern that patients won’t complete the home tests.

The completion rate varies greatly, with the median between 40 and 50 percent.