What is the Difference Between a Colonoscopy and a Sigmoidoscopy?

Choosing the colon cancer screening that’s right for you

by Walter Coyle, MD, Gastroenterologist

Scripps gastroenterologist, Dr. Walter Coyle, helps you to understand the difference between a Colonoscopy and sigmoidoscopy.

by Walter Coyle, MD, Gastroenterologist

Two things you should know right off about colon cancer. First, it is one of the most common cancers. Second, early detection saves lives.

There are two main procedures to screen for colon cancer — colonoscopy and flexible sigmoidoscopy. But which is better? This question has caused some debate in the medical community, but from a consumer perspective, that can be a distraction. The bottom line is, whichever method you choose, get a colon cancer screening.

Comparing colonoscopy and sigmoidoscopy

Colonoscopy and sigmoidoscopy both use a thin flexible tube with a camera at the end to look at the colon. They differ in the areas of the colon they can see. Colonoscopy examines the entire colon, while sigmoidoscopy is a partial exam that only covers the left side of the colon.

Sigmoidoscopy is often easier on patients than colonoscopy. The prep is not as complicated and most people are not sedated during the exam. The problem with sigmoidoscopy is that, sometimes, the portion of the colon being examined is healthy, while there may be problems in the unexamined portion.

The colonoscopy will detect these issues, the sigmoidoscopy alone will not. A recent study found that a significant number of patients who had no problems with the left side of the colon, had issues in other areas.

Additional screening

If you decide to get a sigmoidoscopy over a colonoscopy, make sure you also get a fecal occult blood test (FOBT), which can find cancer in all areas of the colon.

Screening should begin at age 50, unless you have a family history of colon cancer, in which case it should begin earlier. Colonoscopy should be done every ten years, Sigmoidoscopy and FOBT every five years.