A sigmoidoscopy is a screening test that allows a doctor to see inside the sigmoid, or lower part (about 20 inches) of the colon (also called the large intestine). It is frequently used as a screening test to find polyps, which are small growths that may become cancer. Usually polyps do not cause any symptoms and can only be detected by doing a screening test like a sigmoidoscopy. Removing these polyps may prevent colorectal cancer.

About the procedure

During a sigmoidoscopy, the doctor inserts a sigmoidoscope (a thin, flexible fiber optic tube) into the anus. The tube is slowly moved through the rectum and into the lower part of the colon. The doctor views the inside of the colon through the scope or an image from the scope on a video monitor. When the examination is complete, the sigmoidoscope is slowly removed from the body.

The medical team

Most sigmoidoscopies are performed by a gastroenterologist (a doctor who specializes in the function and disorders of the gastrointestinal tract, including the stomach, intestines, and associated organs) or a surgeon, though they are also performed by a primary care physician, such as a general practitioner or internal medicine doctor. A nurse practitioner or physician's assistant may also be qualified to perform the procedure. A nurse will generally assist the doctor and help make you more comfortable.

Surgeon. All surgeons have completed medical school and undergone additional specialized training after medical school. Most surgeons have also passed national level examinations given by a board of surgeons for "board certification." A surgical oncologist is a doctor who specializes in surgery and other invasive procedures to prevent, diagnose, and treat cancer.

Gastroenterologist. All gastroenterologists have completed medical school and undergone five to six years of specialized training in gastroenterology (the study of the normal function and diseases of the esophagus, stomach, small intestine, colon and rectum, pancreas, gallbladder, bile ducts, and liver).

Questions to ask your doctor

Before a sigmoidoscopy, consider asking your doctor the following questions:

• Who will perform the sigmoidoscopy, and who else will be in the room?
• What will happen during the sigmoidoscopy?
• How long will the procedure take?
• Will it be painful?
• Will I be given general or local anesthesia?
• Is there a risk of infection, bleeding, or other adverse effects after the sigmoidoscopy?
• Will I need to avoid any activities after the sigmoidoscopy?
• When will I learn the results?
• Who will explain the results to me?
• What further tests will be necessary if the test results indicate cancer?

Preparing for the procedure

Your doctor or nurse will give you detailed instructions on how to prepare for your sigmoidoscopy, and where and when to arrive for the test.

Review with your doctor or nurse what you should or should not eat or drink before your sigmoidoscopy, and whether you should take your regular medications that day. In addition, tell your doctor about all medications you are taking, as well as any drug allergies or other medical conditions you have. You may need to stop taking medications that increase your risk of bleeding, such as aspirin or blood thinners, for a few days prior to the sigmoidoscopy.

You will be asked to sign a consent form that states you understand the benefits and risks of the sigmoidoscopy and agree to have the test done. Talk with your doctor about any concerns you have about the sigmoidoscopy.

Completely cleansing your lower colon is necessary for a thorough examination. To clean your colon, you will be required to give yourself one or two enema the night before or the day of the sigmoidoscopy. You may also need to follow a liquid diet for up to 24 hours before the procedure, which means eating only foods such as fat-free bouillon or broth, black coffee, strained fruit juice, or gelatin.

During the procedure

A sigmoidoscopy usually takes about 15 to 20 minutes to complete. It is generally performed without anesthesia or sedation (giving a tranquilizing medication), though sedatives may be used if you are particularly anxious about the procedure. You will change into a hospital gown.

You will lie on your side on an examining table in a private room, with a sheet draped over your body. The doctor will gently insert the lubricated scope into your rectum, then view the inside of your colon either through the scope itself or on a video monitor attached to the scope. The doctor will use the scope to blow air into your colon to inflate it for a better examination; this may make you feel bloated or like you need to move your bowels.

If a polyp is found in your colon, your doctor may remove a piece of tissue or the entire polyp, using a tool attached to the end of the sigmoidoscope. A sample of the tissue will then be examined under a microscope by a pathologist (a doctor who specializes in interpreting laboratory tests and evaluates cells, tissues, and organs to diagnose disease) to determine if it is cancerous. If polyps are found during the sigmoidoscopy, your doctor will recommend evaluation of the remaining 4 to 5 feet of the colon not visible during a sigmoidoscopy, as there is a higher likelihood of polyps elsewhere in the colon in this circumstance.

Generally, a sigmoidoscopy is uncomfortable but not painful. If it becomes painful, tell the doctor, and the doctor may be able to reposition the scope.

After the procedure

You will be able to resume your normal activities immediately after the sigmoidoscopy. Unless you were given a sedative, you will be able to drive yourself home.

Following a sigmoidoscopy, you may feel cramps or bloating, but that discomfort usually passes quickly. You may also have a small amount of bleeding from your rectum, which is normal. If you have abdominal pain, major bleeding, dizziness, weakness, or a fever, you should call your doctor.

Additional resources

National Digestive Diseases Information Clearinghouse, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health: Flexible Sigmoidoscopy (November 2004)

MedlinePlus Tutorial: Sigmoidoscopy

American Cancer Society (ACS): Frequently Asked Questions About Colonoscopy and Sigmoidoscopy