"...a Canadian study, published Tuesday in the journal Annals of Internal Medicine, found the test, while still widely recommended, was much less accurate than anyone expected.
In the new study, the test missed just about every cancer in the right side of the colon, where cancers are harder to detect but about 40 percent arise. And it also missed roughly a third of cancers in the left side of the colon.
Instead of preventing 90 percent of cancers, as some doctors have told patients, colonoscopies might actually prevent more like 60 percent to 70 percent."
What to do?
One solution, supported by six studies, is to be sure there is just a short time between when patients finish taking the strong laxative that cleanses their bowel and the colonoscopy, Dr. Rex said. That usually means taking half of the laxative the night before the screening test and the rest in the morning, something that often is not done, he added, but that he and others recommend.
Cancer may also be different in the right colon, researchers said.
Flat and indented polyps tend to cluster in the right colon. And so do another kind, serrated lesions, which, some studies indicate, might turn into cancer much more quickly than typical polyps.
patients should be compulsive about their bowel prep and be sure the test is done by one of the best colonoscopists in their area, gastroenterologists said. Doctors should find polyps in at least 25 percent of men and 15 percent of women. They should take at least eight minutes to withdraw an endoscope from the colon. And they should do a high volume of screening. Dr. Smith said a high volume was at least three or four colonoscopies a day.
After the test, patients can ask whether the doctor got to the right side of the colon and how that was documented.