Approved by the Cancer.Net Editorial Board, 03/2013

A sigmoidoscopy is a screening or diagnostic test that allows a doctor to see inside the lower 20 inches of the sigmoid colon and rectum (also called the large intestine), which plays an important role in the body’s ability to process waste.

During a sigmoidoscopy, the doctor inserts a sigmoidoscope (a pencil thin, flexible tube with a light and a camera) into the anus (the opening at the end of the large intestine, where bowel movements leave the body). The tube is slowly moved through the rectum (the final portion of the large intestine, which stores waste) and into the lower part of the colon. The doctor views the inside of the colon through the scope or on a video monitor.

A sigmoidoscopy is often used to find intestinal polyps, which are small abnormal growths that may become cancerous, as well as to screen for colorectal cancer. It can also be used as a diagnostic test for patients who have rectal bleeding, a change in bowel habits, or other symptoms.

The medical team

Most sigmoidoscopies are performed by a gastroenterologist with the help of a nurse in a doctor's office or at a hospital. A gastroenterologist is a doctor who specializes in the gastrointestinal tract, including the stomach and intestines. However, sigmoidoscopies are also performed by primary care physicians, such as a general practitioner or internal medicine doctor. A nurse practitioner or physician assistant may also be qualified to perform the procedure.

Preparing for the procedure

When you schedule your appointment, you will be given detailed instructions about how to prepare for your sigmoidoscopy, including when and where to arrive for the test. Tell your doctor about all medications and supplements you are taking, and ask whether you should take them on the day of the test. You may need to stop taking medications that increase your risk of bleeding, such as aspirin or blood thinners, for a few days before the sigmoidoscopy. In addition, discuss any drug allergies or other health conditions you may have.

Because your lower colon must be completely clean for the doctor to examine it, you will need to use one or two enemas (a process that involves injecting liquid into the anus to cause bowel movements) or very strong laxatives 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 only eating foods such as fat-free bouillon or broth, black coffee, strained fruit juice, or gelatin.

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

Finally, check with your insurance provider to find out whether the sigmoidoscopy is covered under your plan or if there will be additional out-of-pocket costs.

During the procedure

When you arrive for your sigmoidoscopy, you will need to remove your clothing and change into a hospital gown. The doctor will ask you to lie on your side on an examining table, and a sheet will be draped over your body. Then the doctor will gently insert the lubricated scope into your rectum. The doctor will use the scope to blow air into your colon, which inflates it, making it easier to examine. You may feel bloated or like you need to go to the bathroom.

Generally, a sigmoidoscopy is uncomfortable but not painful. As a result, a sigmoidoscopy is usually performed without anesthesia (medication that blocks awareness of pain). However, sedatives (medication that causes drowsiness) may be used if you are anxious about the procedure. If you start to feel pain at any time during the procedure, tell the doctor so he or she can reposition the scope.

A sigmoidoscopy usually takes about 15 to 20 minutes to complete.

If a polyp is found in your colon during the exam, the doctor will 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 be sent to a laboratory where it will 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 whether it is cancerous. Because finding polyps in the lower part of the colon means there is a higher chance of having polyps elsewhere in the colon, your doctor will likely recommend a colonoscopy to evaluate the remaining four to five feet of the colon that is not examined during a sigmoidoscopy. A colonoscopy is similar to a sigmoidoscopy, except that it allows the doctor to look at the entire colon.

After the procedure

You can expect to return to your normal activities immediately after the sigmoidoscopy, including driving, unless you were given a sedative. If you plan to use sedatives, arrange for a friend or family member to drive you home because you will be groggy from the medication after the procedure.

Initially, you may feel cramps or bloating, but that discomfort usually passes quickly. People will often expel the gas that was put into the colon to inflate it as part of the procedure and may have some diarrhea as the gas is being released. You also may 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.

Questions to ask your doctor

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

  • Who will perform the sigmoidoscopy? Will anyone else be in the room during the procedure?
  • How do I need to prepare for the procedure? Are there any restrictions on what I may eat or drink the day before?
  • What will happen during the sigmoidoscopy?
  • How long will the procedure take?
  • Will it be painful?
  • What are the benefits and risks of having a sigmoidoscopy?
  • Will I be given sedatives or anesthesia?
  • Will I need to avoid any activities after the sigmoidoscopy?
  • Will I need to have someone drive me home from the procedure?
  • When will I learn the results?
  • How will the results be communicated to me?
  • Who will explain the results to me?
  • Will I need any additional tests?

More Information

Tests and Procedures

Endoscopic Techniques

Cancer Screening

Guide to Colorectal Cancer

Additional Resources

National Digestive Diseases Information Clearinghouse: Flexible Sigmoidoscopy

National Cancer Institute: Colorectal Cancer Screening