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, 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 colon. The colonoscope can be used to look at the whole colon and the lower part of the small colon. 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:

• Find problems or diseases of the anus, rectum, or colon. These tests are often done to because you have had problems such as bleeding from the rectum, ongoing diarrhea or constipation, blood or pus in the stool (feces), or ongoing lower belly pain.
• Check the colon after abnormal results from a stool test or a barium enema test.
• Check for colorectal cancer or polyps.
  • Most experts, including the American Gastroenterological Association, recommend that people with no risk factors for colorectal cancer start screening tests 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.

Colonoscopy also may be done to:

• Check for colon or rectal cancer that has come back in people who had treatment.
• Watch the growth of polyps that cannot be completely removed.
• See whether treatment of inflammatory bowel disease is working.
• Take out polyps or take tissue samples (biopsy).
• Take out foreign bodies.
• Check for the cause of chronic diarrhea.
• Check for the cause of bleeding inside the colon.