Sigmoidoscopy – Simpler than Colonoscopy, Still Finds Most Cancers

Doctors urge all persons ages 55 – 75 to be screened for colon cancer by colonoscopy once every ten years. Only around 60% comply with this recommendation, and the main reason given is patient dread of the preparation for the test. The colonoscopy itself is performed under anesthesia so it isn’t an unpleasant experience itself. However the preparation for a colonoscopy involves a “liquid fast” the day before – nothing but clear liquids. Perhaps worse than that, one must also drink a gallon (4L) of a slippery solution of polyethylene glycol (PEG), to completely cleanse the digestive tract. Although the PEG comes with flavoring, it doesn’t make drinking that amount of a laxative a pleasant experience. A person should also stay close to a bathroom all that day, because what goes in will come out, and surprisingly quickly. Less severe preparations have given acceptable results in preliminary tests, but the American Society of Gastroenterologists continues to recommend the full routine as the best colonoscopy preparation.


So is there a screening alternative for the more reluctant patients? Yes there is, and it’s the sigmoidoscopy, referring to the term for the lower third of the large intestine, the “sigmoid colon.” Although this procedure doesn’t see as far up into the colon, at least 50% of all tumors occur in this last stretch of our digestive tracts. A study published in May by the New England Journal of Medicine (NEJM) concluded that sigmoidoscopies can still significantly lower the rate of colon cancer. A large patient group receiving only sigmoidoscopy was followed for many years and compared to people who had not been screened. Patients receiving sigmoidoscopies had 21%, lower rates of colon cancer, and 26%, fewer deaths from colon cancer than the non-screened group. Clearly these patients had benefited from the simpler screening method.

By contrast, a study earlier this year on colonoscopy, also published in NEJM, found the colon cancer death rate in those receiving the examination was over 50% lower than in those not screened. So, colonoscopy remains the more sensitive exam, consistent with it screening the entire length of the colon. The importance of the sigmoidoscopy study nonetheless remains two-fold: First, it is the biggest study of its kind ever performed, and gave better results (decrease in death rate) than many expected. Secondly, a sigmoidoscopy is a much less costly test and one that people are more willing to undergo – with only a simple enema required.

Doctors thus far seem to be in two camps regarding this study. Some compared it sarcastically to mammography of a single breast. Others are mindful of many patients’ anxieties about colonoscopy and taking a more understanding approach. In an editorial in the same NEJM issue as the article, Dr. John Inadomi of the University of Washington in Seattle, was sympathetic to patient feelings, pointedly stating “In this case, the best test is the one that gets done.”

So, to be completely assured you don’t have colon cancer – or pre-cancerous polyps – you should get a colonoscopy, and remember nobody has died of the liquid diet and large volume of PEG laxative. But if you just can’t stomach that, you should definitely get a sigmoidoscopy, because it’s still a good test and definitely better than nothing.