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Colorectal Cancer Screening

What is colorectal cancer screening?

Colorectal cancer screening is a check for cancer of the rectum and colon (large intestine).

Why is it important?

Colorectal cancer is the second leading cause of cancer deaths in the US. Yet it is one of the few cancers that can be prevented. Colorectal screening checks for polyps as well as cancer. Polyps are growths inside the bowel that sometimes become cancerous. When polyps are found early, they can be removed before they become cancerous.


Colorectal screening tests can find cancer in its early stages, before it causes symptoms. If cancer is found early, it can often be cured by surgery. Unfortunately, usually because of no screening, colorectal cancer is often found too late for a cure.

What are the screening tests?

Several tests may be used to check for colorectal cancer.

  • FOBT (fecal occult blood test) is a lab test of a sample of bowel movement (stool). It looks for traces of blood in the stool. Your provider will give you 3 test cards. You will then collect tiny samples of stool at home on 3 different days. You will put the samples on the cards and return the cards to your provider's office. The samples will be tested for blood.

    This test is simple and does not cost much. There are 2 basic types of stool blood tests. The original type is usually referred to as FOBT. Many things can affect its accuracy. When the FOBT finds blood, more tests need to be done to look for the cause.


    Eating certain foods before this test may cause incorrect results. For 2 days before you test your stool, don't eat turnips, horseradish, or red meat. Also, don't take vitamin C, iron supplements, or anti-inflammatory medicines, such as aspirin, ibuprofen, or naproxen, for 2 to 3 days before the test. If you have been taking these medicines daily, ask your provider if you should stop them for a few days before your test. Never stop your medicines without first asking your provider.


    A newer test called the fecal immunochemical test (FIT) is done the same way as the FOBT except that a different chemical is used to test the stool samples. For the FIT you do not have to avoid some foods or medicines before you collect the stool samples.


    Ask your healthcare provider about the instructions for your specific test. And remember that some conditions other than cancer, such as an ulcer, can cause a positive stool blood test.

  • Flexible sigmoidoscopy and colonoscopy use a thin, flexible, lighted tube to check the rectum and colon for polyps and cancer. The scope is put into the rectum. Sigmoidoscopy checks the rectum and lower part of the colon. Colonoscopy uses a longer scope and can check most or all of the rectum and colon. Your healthcare provider can use the scope to remove polyps or other tissue. The tissue will be checked in the lab.
  • Virtual colonoscopy is a way to look at the colon without putting a scope into the rectum. Pictures of the colon are taken using X-rays and a computer (computerized tomography, or CT). This test is not yet widely available, and it has not been shown to be as accurate as actual colonoscopy. If abnormal tissue is seen with this test, then you will need a regular colonoscopy.
  • Double-contrast barium enema uses barium and X-rays to check the rectum and colon. Barium is a fluid that can be seen on X-rays. A tube is inserted into your anus. Barium is passed through the tube into your rectum and colon. The flow of barium in the colon can be seen with a fluoroscope, which is a special X-ray machine. Other names for this test are air contrast barium enema, lower gastrointestinal (GI) exam, and lower GI.

For all but the FOBT you will need to prepare for the test the day before. You will probably not be allowed to eat any solid foods during this time. You will need to take liquids only and use a laxative or enema to clean out your bowel before the test. This allows your healthcare provider to see all of the tissue lining the colon.

When should I have screening tests for colorectal cancer?

If you are 50 to 75 years old and have an average risk of colon cancer, you should be screened with 1 of these 3 methods:

  • Have your stool checked for blood with a fecal occult blood test once a year.
  • Have a sigmoidoscopy exam every 5 years with fecal occult blood testing at least every 3 years between the 5-year exams.
  • Have a colonoscopy every 10 years. If you have not recently had a colonoscopy and the results from other tests show blood or abnormal tissue, then you will need to have a colonoscopy to check for cancer.

Barium enema may be done every 5 years instead of colonoscopy or sigmoidoscopy. There is no evidence that this test is as effective as the tests listed above, but this test may be preferable to colonoscopy if you have certain colon conditions.


At this time a virtual colonoscopy cannot be recommended as a known effective screening test.


If you have a parent, brother, or sister who has had polyps or cancer in the colon, especially before they were 50 years old, you may have a higher risk for polyps or cancer. Your healthcare provider may want to start screening you before you are 50. You may also need to be checked more often.


Ask your provider when and how often you should be tested for colorectal cancer.


Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.


HIA File diag5112.htm Release 13/2010

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