Q: How often should a healthy 55-year-old woman have a colonoscopy? Do the benefits outweigh the risk of complications, such as bowel perforation?

A: Colonoscopy is one of several tests used to screen for colorectal cancer, the third most common cancer and cause of cancer mortality (after breast and lung cancer) in American women. In 2008, some 149,000 Americans were diagnosed with the disease, and 50,000 died of it. Experts believe that adequate screening could have prevented perhaps 60 percent of those deaths.

How often you should be screened depends on the test and your risk for colon cancer. If you're at average risk and choose colonoscopy, you should have the procedure every 10 years, starting at age 50. Colonoscopy may be performed earlier and more often in people at increased risk, including those with a personal or family history of polyps or colorectal cancer, inflammatory bowel disease, or a hereditary syndrome such as familial adenomatous polyposis or hereditary nonpolyposis colorectal cancer (Lynch syndrome).

Colorectal cancer screening generally starts at age 50 because colon cancer risk increases with age, and more than 90 percent of cases occur in people ages 50 and over. Most colorectal cancers arise from what are known as adenomatous polyps. The progression from precancerous polyp to full-blown cancer is believed to take 10 years or more, though we don't really know, because clinicians remove polyps when they find them. Screening allows them to remove polyps before they become cancerous and to identify cancer itself early, when it's most treatable.

Colonoscopy finds more polyps and cancers than other methods and permits their immediate removal or biopsy. But there are some downsides: it's expensive, and insurance doesn't always cover the cost; the bowel preparation done in advance is unpleasant; and most patients are sedated during the procedure, so they can't go home on their own afterward. Moreover, in one of every 400 colonoscopies, there are complications—serious bleeding, colon perforation, infection, abdominal pain, or a cardiovascular event.

If you're concerned about the possibility of complications, you can choose a different screening method. In 2008, several agencies issued guidelines on the various strategies for colorectal cancer screening and the frequency with which they should be performed (see chart). CT colonography ("virtual colonoscopy") may be an option for you. It's relatively new, so there's less evidence on its safety and effectiveness than there is for colonoscopy and some of the other methods. But this test is gaining increasing acceptance. It involves the same bowel preparation as colonoscopy, but no colonoscope is inserted, and no sedation is required. Colonoscopy is needed in addition only if a polyp or other abnormality is found.

Some guidelines recommend that routine screening continue until age 76, with screening an option between ages 76 and 85, depending on overall health and risk factors. Screening is not recommended after age 85.

If you choose colonoscopy, seek out a gastroenterologist with plenty of experience performing the procedure and a facility equipped to handle potential problems.

Colorectal screening options for people at average risk

Test

How it's performed

How often (recommended by)

Fecal occult blood test (FOBT)

Lab test on stool sample

Annually (USPSTF, ACS)*

Sigmoidoscopy

Direct view of lower third of colon

Every 5 years** (USPSTF, ACS)

Colonoscopy

Direct view of entire colon

Every 10 years (USPSTF, ACS)

Double-contrast barium enema

X-ray of entire colon

Every 5 years (ACS)

CT colonography

CT scan of entire colon

Every 5 years (ACS)

Fecal DNA

Lab test on stool sample

Not determined (ACS)

*USPSTF=U.S. Preventive Services Task Force on Screening for Colorectal Cancer, November 2008. ACS=Joint Guideline from the American Cancer Society, the U.S. Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology, March 2008.

**The USPSTF recommends combining sigmoidoscopy every five years with FOBT every three years.