What is a Flexible Sigmoidoscopy?

Flexible sigmoidoscopy is often performed as an alternative to regular colonoscopy if the lower part of a patient’s large intestine and your rectum need to be checked for signs of colon cancer. While a procedure called rigid sigmoidoscopy does exist, it’s definitely not as popular as the flexible test. Doctors referring to the procedure simply as sigmoidoscopy are most likely talking about flexible sigmoidoscopy.

Sigmoidoscopy is performed by putting a bendable tube called a sigmoidoscope into the anus and guiding up the rectum and sigmoid colon. The patient will be asked to lie on his or her left side on top of an exam table while the sigmoidoscope is being used. Sigmoidoscopes have a diameter of roughly the size of a human finger and have a camera and a light attached to the end, which the doctor will use to examine the colorectal wall while the device is withdrawn from the body. The procedure as a whole is not painful, as many patients are sedated first. You may feel a little bit of pressure, cramping and bloating during the test, but this is normal.

Is a Sigmoidoscopy Better Than a Colonoscopy?

Whereas a colonoscopy allows the GI doctor to look at the entirety of the large intestine, a sigmoidoscopy is limited to the lower portion of the large intestine only. There is a greater risk of missing a cancerous polyp or other abnormality with sigmoidoscopy than colonoscopy—and the doctor will definitely not be able to detect polyps found higher up than the sigmoid colon during the procedure.

Nevertheless, if something suspicious is detected in the rectum or sigmoid colon, then a doctor will be able to perform polyp removal, biopsy, or whatever other procedure is necessary—as he or she would be able to do during a regular colonoscopy. If the polyps are too big, however, they may need to be removed during a later appointment, probably a colonoscopy exam that will let the doctor look at other sections of the colon for similar growths. The risks of both procedures is relatively low, although you should notify your medical provider immediately if you notice signs of bleeding or experience high fevers or severe abdominal pain during the recovery process.

Do I Still Need to Do Bowel Prep?

Before any colon screening procedure, all patients must practice bowel prep. Sigmoidoscopy is no different. The bowels must be completely empty so that the endoscopist (GI doctor or other doctor performing the sigmoidoscopy) will be able to see the colorectal walls clearly. Fecal matter left inside the colon will obstruct the doctor’s view and might produce false positive results if the food likes like a polyp or a tumor. In order to empty the bowels, simply stop eating solid foods and non-clear liquids 24 hours before your appointment. You’ll also be given approximately 4 liters of drinkable laxative that will encourage frequent bowel movements before your exam. During this time, please remember to drink plenty of clear beverages, such as water or lemonade, and refrain from any fruit juices that have colored dye in them, as the dye can stain the bowel tissue and botch results.


Reviewed 12/29/2011 by David M. Nolan, M.D.
Diplomate of the American Board of Internal Medicine, 2011
Currently a Fellow of Gastroenterology, at UCI 2011-2014