Many Americans are still failing to get two of the most effective tests for catching colon cancer early, according to researchers with the American Cancer Society.

Their study of more than 129,000 Americans age 50 and up found that only 42 percent of men and 31 percent of women had ever undergone colon cancer screening with sigmoidoscopy or colonoscopy.

Others had gone through the procedures not as a screening measure, but as a diagnostic test to investigate signs and symptoms like blood in the stool or abdominal pain.

That so few people had been screened came as a surprise, study co-author Dr. Michael J. Thun of the ACS in Atlanta told AMN Health, because the group was participating in a cancer prevention program and was generally more “health conscious” than the U.S. norm. Rates of screening with sigmoidoscopy and colonoscopy are “certainly” even lower in the general U.S. population, he said.

Thun and his colleagues report the findings in the American Journal of Public Health.

Colon cancer is one of the top cancer killers in the U.S., but experts believe that many of these deaths could be prevented if all older adults underwent regular screening. The ACS and other medical organizations advise people at average risk of the disease to begin screening at age 50; those at heightened risk, due to factors such as family history of the disease, may need to begin earlier.

Sigmoidoscopy and colonoscopy both involve inserting a thin, flexible, optical tube into the colon to look for cancer or polyps, which are growths that can become cancerous. Sigmoidoscopy investigates only the lower portion of the colon, while colonoscopy inspects the whole organ.

The ACS recommends that people either get sigmoidoscopy every five years - ideally in combination with yearly tests for blood in the stool - or colonoscopy every 10 years. An alternative is to get a test called the double-contrast barium enema every five years; in this procedure, barium sulfate and air are pumped into the colon through a tube in order to fill and expand it for X-ray studies.

The new study is not the first to find low rates of sigmoidoscopy and colonoscopy among Americans. Thun said that a number of reasons are likely playing a role, not the least of which is the fact that “huge numbers” of people are thought to be unaware of the availability and effectiveness of colon cancer screening.

“Part of what led to the increase in mammography,” Thun said, “was that women started asking for it.”

Another factor he pointed to is health insurance. Private plans vary in their coverage for screening, and in this study, men and women who lacked insurance altogether, not surprisingly, were less likely to undergo sigmoidoscopy or colonoscopy.

In addition, people between the ages of 50 and 64 were less likely than older men and women to be screened. The researchers speculate that health insurance coverage may partially explain the difference, since Americans age 65 and older are covered by Medicare, which helps pay for colon cancer screening.

SOURCE: American Journal of Public Health, October 2004.