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Colorectal Cancer: Screening

Screening means checking for cancer before a person has symptoms. Regular screening is very important for colorectal cancer because it can often find cancer early, when it is likely to be easier to treat. In fact, screening can even prevent many colorectal cancers. That’s because screening lets the healthcare provider find and remove growths inside the colon or rectum (colorectal polyps) before they have a chance to turn into cancer. 

Types of screening tests

Several tests can be used to screen for colorectal cancer. Some of these tests can also find colorectal polyps.

Screening tests to find colorectal polyps and cancer

  • Flexible sigmoidoscopy. This test looks at your rectum and the lower part of your colon. Your healthcare provider inserts a thin, lighted tube with a small video camera on the end into your rectum. The tube is called a sigmoidoscope. He or she looks for polyps or other abnormal areas. These can be removed and sent to a lab for testing.

  • Colonoscopy. This test looks at your rectum and your entire colon. It uses a colonoscope, which is a long, lighted tube with a small video camera on the end. The provider inserts the scope into your rectum and up into your colon. The provider looks for polyps or other abnormal areas. These can be removed and sent to a lab for testing. This test usually requires sedation, where you are given medicine to make you sleepy during the test. A colonoscopy is the only test that lets the provider see the entire colon and rectum, and remove pieces of any abnormal areas for testing. If you have any of the other tests and something uncertain is found, you will likely need a colonoscopy. 

  • Virtual colonoscopy (CT colonography). This test is a special type of CT scan of the colon and rectum. Once the CT images are taken, a computer combines them to create a 3-D picture. This lets the provider look for polyps or cancer.  

Screening tests to find cancer only

These tests look for signs of cancer in your stool or feces. These tests can be done at home. But they are less likely to find polyps. And they must be done more often than the tests above.

  • Fecal occult blood test (FOBT) or fecal immunochemical test (FIT). These tests look for hidden or occult blood in the stool. Blood vessels in cancers and sometimes in polyps are easily broken during a bowel movement. This may cause blood to show up in your stool. For these tests, you collect a small amount of your stool with a brush or wooden applicator. Then you smear it on a special card that can find blood. In most cases you need to do this for a few bowel movements in a row. You then send the cards to your provider’s office or to a lab.

  • Stool DNA test. This test looks for DNA changes in cells in the stool that might be signs of cancer. It also looks for hidden blood in stool. For this test, you collect an entire bowel movement. This is done using a special container put in the toilet. The sample is sent to a lab for testing. 

What expert groups recommend

Expert groups generally advise that people at average risk of colorectal cancer start screening at age 50. But the American Cancer Society recommends starting screening at age 45. Some people are at higher risk for colorectal cancer, based on family history or other factors. They might need to start screening at a younger age, and to be screened more often than normal.

How often you need these tests depends on which test you have. In general, you can go longer between tests if you have a colonoscopy, which lets the doctor find and remove polyps, or similar tests. Screening tests that look for blood or other things in the stool must be done more often.

Not all expert groups recommend all of the screening tests above. For example, virtual colonoscopy and the stool DNA test are still fairly new tests that are not part of the recommendations of all expert groups.

Talk with your healthcare provider

Talk with your healthcare provider about which tests might be right for you. No matter which test you choose, the most important thing is that you get screened. Some of these tests may be uncomfortable and a little embarrassing. But it's important to keep in mind that if cancer is found at an early stage during screening, treatment is more likely to work well. Many cancers can even be prevented with these tests. 

Note: If you have a test other than a colonoscopy and have an abnormal test result, you will need to follow-up with a colonoscopy.

Online Medical Reviewer: Alteri, Rick, MD
Online Medical Reviewer: Gersten, Todd, MD
Date Last Reviewed: 12/1/2017
© 2013 The StayWell Company, LLC. 800 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare provider's instructions.