Colorectal Cancer Health Center

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 48 in. (122 cm) to 72 in. (183 cm) 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.

Colonoscopy is one of many tests that may be used to screen for colon cancer. Which screening test you choose depends on your risk, your preference, and your doctor. Talk to your doctor about what puts you at risk and what test is best for you.

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

Colon Cancer: Which Screening Test Should I Have?

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Why It Is Done

Colonoscopy is done to:

• Check for colorectal cancer or polyps.
  • Tests are recommended by the American Cancer Society (ACS), the American College of Gastroenterologists (ACG), the American Gastroenterological Association (AGA), and the U.S. Preventive Services Task Force (USPSTF).
  • These groups recommend routine testing for people age 50 and older who have a normal risk for colorectal cancer.
  • Your doctor may recommend earlier or more frequent testing if you have a higher risk for colorectal cancer. Talk to your doctor about when you should be tested.
• 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.