Pros and cons: This is the only test where the doctor can see the entire colon and find and remove polyps or abnormal tissue, all in one procedure. Leddin says it is the only test appropriate for people who are at high risk. But with this procedure, there is a one-in-1,000 risk of perforating the bowel. The test can be more difficult for older people and those with diverticular disease, an inflammation in the colon.

Flexible Sigmoidoscopy. The “flex sig” is similar to the colonoscopy, except the tube is shorter and goes only about half as far, into the lower part of the colon. Usually there is no sedation, and you just have to use a mild laxative or enema before the test.

Pros and cons: Polyps and abnormal tissue can be removed from the lower colon during the procedure. The risk of perforation is less than with a colonoscopy, says Leddin, but the test cannot detect polyps or tumors higher up in the colon.

Double-Contrast Barium Enema. You have a series of X-rays to provide views of the entire colon. A radiology technician performs the test, which includes inserting liquid barium and air through a tube in the rectum. The barium mixture makes the colon walls visible. You do not need sedation, but before the test, you have to clean out the colon, similar to preparation for a colonoscopy.

Pros and cons: Leddin says the test is “pretty good” at detecting polyps and cancer. But it is not possible to remove polyps, tumours or abnormal-looking tissue during the procedure. If any are found, you will need a flexible sigmoidoscopy or colonoscopy.

In addition to these four screening methods, there is an important exam that your family doctor can do during your regular checkup: a digital rectal examination, inserting a gloved finger into the rectum to feel for abnormalities. Stein says it should not be considered a substitute for other screening, but it can be used in conjunction with other tests. “Having a digital rectal exam is important because there are many rectal cancers.”

The Future of Testing

“The new kid on the block is virtual colonoscopy using a CT scan,” says Leddin. Instead of inserting a tube into the colon, the procedure uses a computerized tomography (CT) scan to produce 3-D images of the colon and detect polyps or tumours. Leddin adds, “The advantage is it can be done by a technician. There is no risk of a perforating tear in the bowel.”

You still have to clean out your colon and, although the test does not require sedation, it can be uncomfortable. If polyps or other abnormalities show up, a colonoscopy is needed to remove them. Although the new test is not widely available for screening in Canada yet, Leddin says, “I think, in future, screening will be done on a mixture of occult blood and virtual colonoscopy, and the real colonoscopy will be largely reserved for people who have abnormalities either on the blood testing or the CT scan.”