Colon Cancer Screening: Don't Delay It

Plus, two of the other three screening tests for colon cancer (flexible sigmoidoscopy and double contrast barium enema) also require a bowel prep and neither is as sensitive as the colonoscopy. And here's the irony: If they show polyps or cancers, you'll still need a colonoscopy to evaluate and/or remove them for evaluation.

The one test that doesn't require prep is a fecal occult blood test. With this test, you collect stool samples, which are tested for breakdown products of blood in stool. You have to abstain from iron pills, red meat or broccoli before the test, and it still has a high rate of false positives. Plus, you have to do it three times. "Fecal occult blood tests probably pick up problems 50 to 60 percent of the time," says Dr. Stein, which, of course, means it misses about half of all cancers. And if it's positive, you still need a colonoscopy.

A newer stool test evaluates the stool for DNA from the most common mutations found in colon cancer and large polyps. That test, Dr. Stein says, is about 85 percent effective. However, it's still considered experimental and most insurances do not cover it.

One day, Dr. Stein predicts, colonoscopy will take a back seat to an improved DNA fecal occult blood test, or to a virtual colonoscopy, in which your colon is examined via a CT or MRI. Right now, however, you still have to do a colon prep for an MRI or CT, and they're not covered by insurance either unless you cannot undergo colonoscopy for some reason. And you face the same issue with the virtual colonoscopy as you do with any other non-colonoscopy test: If it finds something suspicious, you still need a colonoscopy to remove the "something" for testing.