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 provider find and remove growths inside the colon or rectum (colorectal polyps) before they have a chance to turn into cancer.
Screening tests for colorectal cancer
Several tests can be used to screen for colorectal cancer. Some of these tests can also find colorectal polyps.
Screening tests that can find colorectal polyps or cancer
Flexible sigmoidoscopy. This test looks at your rectum and the lower part of your colon. For this test, your provider inserts a thin, lighted tube with a small video camera on the end into your rectum. The tube is called a sigmoidoscope. The provider 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 through 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 made sleepy during the test.
Double-contrast barium enema. This test is also called an air-contrast barium enema. A chalky white liquid called barium is put into the rectum through a small, flexible tube. This liquid coats the lower part of your intestine, making it easier to see during X-rays. Air is also pumped in to expand the colon and rectum. Then a technician takes a series of X-rays to show any problems in your colon and rectum.
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 that mainly find cancer
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 less often 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.
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.
What expert groups recommend
Expert groups generally advise that people at average risk of colorectal cancer start screening at age 50. 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 be effective. Many cancers can even be prevented with these tests.