Colonoscopy is a test that allows your doctor to look at the inner lining of your large intestine (rectum and colon). He or she uses a thin, flexible tube called a colonoscope to look at the colon. A colonoscopy helps find ulcers, colon polyps, tumors, and areas of inflammation or bleeding. During a colonoscopy, tissue samples can be collected (biopsy) and abnormal growths can be taken out. Colonoscopy can also be used as a screening test to check for cancer or precancerous growths in the colon or rectum (polyps).

The colonoscope is a thin, flexible tube that ranges from 48in. to 72in. long. A small video camera is attached to the colonoscope so that your doctor can take pictures or video of the large intestine (colon). The colonoscope can be used to look at the whole colon and the lower part of the small intestine. A test called sigmoidoscopy shows only the rectum and the lower part of the colon.

Before this test, you will need to clean out your colon (colon prep). Colon prep takes 1 to 2 days, depending on which type of prep your doctor recommends. Some preps may be taken the evening before the test. For many people, the prep for a colonoscopy is more trying than the actual test. Plan to stay home during your prep time since you will need to use the bathroom often. The colon prep causes loose, frequent stools and diarrhea so that your colon will be empty for the test. The colon prep may be uncomfortable and you may feel hungry on the clear liquid diet. If you need to drink a special solution as part of your prep, be sure to have clear fruit juices or soft drinks to drink after the prep because the solution tastes salty.

For more information on screening tests for colon cancer, see:

Which test should I have to screen for colorectal cancer?

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Why It Is Done

Colonoscopy is done to:

• Check for colorectal cancer or polyps.
  • Screening tests are recommended by the American Gastroenterological Association, the American Cancer Society, and the U.S. Preventive Services Task Force (USPSTF). These groups advise people who have no risk factors to be tested starting at age 50.
  • The American Gastroenterological Association recommends that people with a family history of colon cancer have a colonoscopy at age 40, or 10 years before the age that the relative got cancer.
  • If you are at increased risk for colon cancer, talk to your doctor about which test is best for you and how often you should have the test.
• Check for the cause of blood in the stool or rectal bleeding.
• Check for the cause of dark or black stools.
• Check for the cause of chronic diarrhea.
• Check for the cause of iron deficiency anemia.
• Check for the cause of sudden, unexplained weight loss.
• Check the colon after abnormal results from a stool test or a barium enema test.
• Watch or treat inflammatory bowel disease (IBD).
• Check for the cause of long-term, unexplained belly pain.