Overview: The Basics

A sigmoidoscopy is an internal exam of the lower part of the large colon using a short, thin, flexible lighted tube ("scope"). It is inserted into the rectum and slowly guided into the colon. The tube, called a flexible sigmoidoscope, has a lens for viewing. It may also have a small biopsy instrument to remove tissue to be checked under a microscope for signs of disease. 

What to Expect: During the Screening

During the test you are positioned on the left side with knees drawn up toward the chest. First, your doctor will do a digital rectal exam by gently inserting a gloved and lubricated finger into the rectum to check for any abnormalities.

Next, the sigmoidoscope is inserted into the rectum, and you will feel some pressure. Air is gently introduced through the scope to expand the colon and help the doctor see well. Your doctor then moves the scope as far as needed to examine the lower colon. As the scope is slowly removed, the lining of the bowel is carefully examined. A hollow channel in the center of the scope allows for the passage of forceps for taking a biopsy if needed.

What can be found?

Your doctor can help you determine the cause of abnormal results and diagnose the cause of diarrhea, bowel obstruction, diverticulosis, inflammatory bowel disease, anal fissures, hemorrhoids as well as find colon polyps that might be in this lower part of the colon.

How to Prepare

The colon and rectum must be completely empty for flexible sigmoidoscopy to be thorough and safe. Some doctors recommend a combination of a laxative and a small enema before the test. Some doctors may advise you to drink only clear liquids for 12-24 hours before the procedure is scheduled. A liquid diet means clear, fat-free bouillon or broth, gelatin, strained fruit juice (no grape juice or any liquid with red color), water, plain and unsweetened coffee or tea, or diet soda. The night before, or even immediately before the flexible sigmoidoscopy, you may be given an enema, which is a liquid solution that washes out the lower intestine.