Careful screening may miss some colon problems, which is why everyone should know their risk.

RODALE NEWS, EMMAUS, PA—According to the National Cancer Institute, there will be nearly 150,000 cases of colon and rectal cancer combined this year in the United States. A colonoscopy—a cancer screening test that uses a small camera to check the colon and rectum—remains the go-to screening method for detecting early signs of these diseases. But new research shows though that colonoscopies may in fact miss more than 7 percent of colorectal cancers.

THE DETAILS: A colonoscopy can prevent the development of colon cancer by removing the precancerous polyps. But researchers at the University of Manitoba found that many of the colorectal cancers diagnosed within three years after a colonoscopy likely began as lesions missed by the initial colonoscopy. The study, published in the American Journal of Gastroenterology, suggests that colonoscopy by general practice physicians, colonoscopy among women, and right-sided colon cancers are associated with a higher likelihood of early/missed colon cancer. Still, says researcher Harminder Singh, MD, MPH, FRCPC, “Colonoscopy is the test of choice when investigating individuals with symptoms, such as older individuals with rectal bleeding.”

WHAT IT MEANS: The procedure remains an important tool for detecting and preventing cancer, but as with other screening tests, colonoscopy has its limitations. Here are some important ways to protect your bowel health:

• Stay on schedule for colonoscopy. For most people, that means routine screenings starting at age 50. Talk to you physician to see if you have any risk factors that call for testing sooner.

• Be alert for symptoms of bowel problems, such as blood in the stool, changes in bowel movements, or abdominal pain.

• Ask about sedation. A 2008 study found that scans were more accurate for patients who were under deep sedation.

• Increase your chances of an accurate colonoscopy by following your doctor’s instructions for colonoscopy preparation. This will involve a complete cleanse by use of enemas and laxatives, and by abstaining from solid foods. Bowel preparation is often worse in the right colon, where there is a higher risk of missed colon cancers; inadequate bowel preparation can heighten that risk.

• For more suggestions, see our story on colonoscopy preparation.