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Colonoscopy

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Having a barium enema within a week before the test. Barium can block your doctor's view of the colon.
  • Not doing a good colon prep before the test. If you still have stool (feces) in the colon, your doctor may cancel the test and you will have to reschedule and do the colon prep again.
  • Having a colon that has many turns, past surgery on the colon, or a lot of pain during the test.
  • Taking iron supplements. This may make your stool turn black and make it hard to clean out the colon. Do not take iron supplements for several days before a colonoscopy.
  • Drinking red or purple fluids, such as grape juice or fruit punch.
  • Eating red or purple foods, such as grape ice pops or cherry gelatin.

What To Think About

  • In general, pregnant women and people who have an abdominal infection or an attack of diverticulitis should not have a colonoscopy unless there is an important reason for it.
  • Colonoscopy is a more expensive procedure than a stool test or other endoscopic colon test (such as sigmoidoscopy), but it can be done less often over time if results are normal.
  • Experts recommend routine colon cancer testing for everyone age 50 and older who has a normal risk for colon cancer.
  • Your doctor may recommend earlier or more frequent testing if you have a higher risk for colon cancer. Talk to your doctor about when you should be tested.
  • Other screening tests for colon cancer include sigmoidoscopy, stool tests, and computed tomographic colonography. 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.

Related Information

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.

  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

  • Levin B, et al. (2008). Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: A joint guideline from the American Cancer Society, the U.S. Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. CA: A Cancer Journal for Clinicians, 58(3): 130–160.

  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.

  • U.S. Preventive Services Task Force (2008). Screening for colorectal cancer: U.S. Preventive Services Task Force recommendation statement. Available online: http://www.uspreventiveservicestaskforce.org/uspstf/uspscolo.htm.

WebMD Medical Reference from Healthwise

Last Updated: December 07, 2011
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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