Single Fecal Test Inadequate for Detecting Colon Cancer

Doctors not using more accurate six-sample home method enough

Serena Gordon

Serena Gordon

Published on January 17, 2005

MONDAY, Jan. 17, 2005 (HealthDayNews) -- A single fecal blood test doesn't detect likely cases of colon cancer nearly as well as a six-pack home test does, yet many doctors continue to rely on the single test.

That's what two large-scale studies by separate research teams -- one looking at the effectiveness of fecal occult blood tests and the other studying how doctors actually use colon cancer screening techniques in their practices -- report in the Jan. 18 issue of Annals of Internal Medicine.

Fecal occult blood tests are used to look for blood in the stool, which can be an indication of colon cancer.

The first study, involving more than 2,500 people, compared the accuracy of two different fecal occult blood tests: a single office-collected stool sample and the six-sample, home-collected test. The home test was far superior, detecting 23.9 percent of likely cancers versus 4.9 percent for the office test.

Despite these differences, a survey of more than 12,000 doctors and patients found that one-third of the doctors still relied solely on the office test rather than sending the six-sample test home with their patients.

"Colon cancer is one of the most important causes of death from malignancy, and after the age of 50, it's important to screen for cancer and polyps," said Dr. Harold Sox, editor of the Annals of Internal Medicine. "Talk about it with your doctor and don't settle for the single-sample test done in the office. Insist upon the six-sample fecal occult blood test."

One of the reasons doctors still rely so heavily on the single test is because there had been no good comparison of the tests until now, Sox added, and doctors may have believed that the single test was as accurate as the home test.

"As far as I know, this is the first very high-quality study that shows the poor performance of the single-sample test," Sox said. "I hope that when doctors read about this study, they'll realize that the single sample in-office approach isn't the right way to go."

The study included 2,665 people from 13 different Veterans Affairs Medical Centers. They were between the ages of 50 and 75, and nearly all were men. None had symptoms of colon cancer.

All of the study volunteers underwent a physical exam and had a single-sample test taken at that time. They were also asked to provide fecal samples for the six-sample test. Finally, they all had colonoscopies, a procedure in which a thin, flexible tube with a light and camera attached to it is inserted into the rectum. The images are then sent back to a monitor so the doctor can view the inside of the colon.

Two hundred and eighty four people had "serious" polyps, which often turn into cancer, said study author Dr. Judith Collins, section chief of gastroenterology at the Veterans Affairs Medical Center in Portland.

The six-sample test accurately predicted those precancerous polyps almost 24 percent of the time, while the single-sample test only found 4.9 percent.

"This is an education issue for both patients and physicians," said Collins. She added that she thinks many doctors use the office test because they thought it was as reliable as the six-sample test, and they were doing the rectal exam for other reasons. And, she said, patient compliance is also an issue.

In the second study, researchers interviewed more than 1,100 primary-care physicians about their colon cancer screening practices. They also interviewed more than 11,000 people over age 50 who were eligible for colon cancer screening to see what types of screening had been performed.

About 25 percent reported having a fecal occult blood test. One-third of those had the in-office test only. Ninety percent of doctors said they used fecal occult blood testing at least once a month and one-third said they relied only on the in-office test.

Ten percent of the patients said they had abnormal fecal occult blood tests, but fewer than 50 percent were referred for further testing.

While the six-sample test was better than the single test, screening guidelines recommend not relying on either test alone. The American Cancer Society recommends an annual fecal occult blood test, plus a flexible sigmoidoscopy every five years, or a colonoscopy every 10 years.

"Colon cancer screening can prevent cancer and save lives," Collins said.

More information

To learn more about colon cancer screening recommendations, go to the American Cancer Society.

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