MARK POCHAPIN, MD: There are a lot of different ways. They're all not equivalent, though. The most effective and most comprehensive would be a colonoscopy, which is a procedure where a tube is put in the intestine, looks around the entire colon. That's also the most invasive, and it's done with sedation, so a patient is relatively sleepy or asleep.
Then there's a sigmoidoscopy, which is a much smaller version of that, where it's just the bottom of the colon that they're looking at. That's usually combined with fecal occult blood testing, which is the little card that doctors or nurses use to see if there's any occult or microscopic blood in the stool.
And then there's a barium enema, which is a radiographic or an x-ray test. And finally, there's a new kid on the block known as virtual colonoscopy, which is really a fancy three-dimensional CAT scan, which still requires the same preparation as colonoscopy, but it's an indirect or an x-ray measurement of the internal view of the colon.
DAVID R. MARKS, MD: How is a person supposed to choose which one of these screening methods is right for them?
JOHN MacDONALD, MD: With good advice. Obviously the patient can't really choose which is the appropriate method for them. Many people feel, nowadays, that if a patient can tolerate a colonoscopy, which most people can, that that's the best approach because, for several reasons. One is that, if you do a colonoscopy and you find that the colon is entirely normal, no polyps, no abnormalities, that has been shown to very substantially decrease the risk of death from colon cancer in the next 7-10 years. So it's a very good screening test.