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  • Digestive system


The sigmoid is the last small stretch of colon (large intestine) before the rectum. A sigmoidoscopy examines this part of the colon as well as the rectum and the anus for abnormalities.

Who is a candidate for the procedure?

This procedure may be done if a healthcare professional knows or suspects that a person has:
  • colorectal polyps, small growths on the walls of the bowel or colon
  • a tumor in the colon or bowel, such as colon cancer
  • bleeding from the bowels, known as gastrointestinal bleeding
  • certain types of colitis, or inflammation of the colon, such as ulcerative colitis, Crohn's disease or irritable bowel syndrome
  • a twist in the lower bowel that is blocking the bowel or causing pain
This procedure is also done to screen for colon cancer in healthy persons starting at age 50. It may be done before age 50 if a person has risk factors, such as a family history of colon cancer.

How is the procedure performed?

Before the procedure, the bowel must be cleaned out to allow a good view. If too much stool is in the lower colon, the doctor will be unable to see the inside walls of the bowel.
Thus, a person will be asked to stop eating at least 8 hours before the procedure. Laxatives and an enema are often given before the procedure. This helps to clear the bowel.
This preparation is very important because if the instructions are not followed, the procedure may have to be repeated. If all goes well, the procedure takes only about 15 to 20 minutes.
It may be done in a clinic, a doctor's office, or the hospital. The person may be given a medication to help him or her relax.
Before the procedure, the person changes into a hospital gown. He or she then lies on an exam table in a special position, such as:
  • on the left side with knees drawn up toward the chest
  • on the back with knees drawn up and the feet in stirrups
During the exam, an endoscope is used to allow the doctor to see the inside of the bowel.
This instrument is a specially constructed tube with a light and camera on the end. The anus is lubricated and the endoscope is passed through it into the rectum. This is somewhat uncomfortable and may cause an urge to defecate.
Puffs of air through the tube are used to help open up the colon. This makes it much easier to get a good view of the tissues.
During the procedure, the healthcare professional can also:
  • remove any colorectal polyps, tiny growths on the walls of the bowel
  • take a sample of tissue to be examined in a lab, known as a biopsy
  • straighten out a loop of twisted colon


Anderson KN, Anderson LE, Glanze WD. Mosby's medical, nursing, and allied health dictionary, 5th ed. St. Louis, Missouri: Mosby-Year Book, Inc., 1998.

Pagana KD and Pagana T. Mosby's manual of diagnostic and laboratory tests, 4th ed. St. Louis: Mosby, 1998.

Report of the U.S. Preventive Services Task Force. Guide to Clinical Preventive Services, 2nd ed. Alexandria, Virginia: International Medical Publishing, Inc., 1996.

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