Several tests can be used to detect colon polyps. Two of these exams, flexible sigmoidoscopy and colonoscopy, also can be used to collect tissue samples (called a biopsy) or to remove colon polyps. All the tests may be used to screen for colon polyps and colon cancer and as follow-up tests after colon polyps have been removed. There are two basic types of tests-stool tests and tests that look inside your body.
- Fecal immunochemical test (FIT). A FIT is done to look for microscopic amounts of blood in the stool. There aren't any restrictions on what you can eat before having this test. If the test is positive for blood in the stool, it is important to have a colonoscopy. This will help your doctor find the source of the blood and remove polyps if they are found.
- Fecal occult blood test (FOBT). An FOBT also looks for blood in the stool, but it isn't as specific as the FIT. There are restrictions on what you can eat before having this test. If this test is positive for blood in the stool, you will need to have a colonoscopy.
A less common stool test is the stool DNA test (sDNA). This test looks at DNA in the stool to see if there are changes in the cells of the colon. Certain kinds of changes in cell DNA happen when you have cancer. If your test is positive, you will need to have a colonoscopy.
By itself, a positive result from a stool test is not evidence of colon polyps or colon cancer. And a negative result from a stool test (no blood found) does not mean that you do not have polyps or colon cancer.
Tests that look inside your body
- Flexible sigmoidoscopy. Flexible sigmoidoscopy allows the doctor to look at the lower third of the colon. During a sigmoidoscopy exam, samples of any growths can be collected (biopsied). And precancerous and cancerous polyps can sometimes be removed. But if your doctor finds polyps, you will need to have a colonoscopy to check the upper part of your colon.
- Colonoscopy. This screening method lets a doctor inspect the entire colon for polyps and cancer. During a colonoscopy, samples of any growths can be collected (biopsied). And precancerous and cancerous polyps usually can be removed.
Another test that is used much less often is computed tomographic colonography (CTC), also called virtual colonoscopy. It uses X-rays to make a detailed picture of the colon to help the doctor look for polyps. If this test finds polyps, you will need to have a colonoscopy.
Screening for colon cancer
Screening for colon cancer with a single test or a combination of tests reduces your chance of having complications and dying from colon cancer. Experts recommend routine colon cancer testing for everyone between the ages of 50 and 75 who has a normal risk for colon cancer. People with a higher risk, such as those with a strong family history of colon cancer, may need to be tested sooner. Talk to your doctor about when you should be tested.
If you are between the ages of 50 and 75, screening may lower your risk of dying from colon cancer. Screening options include the following commonly used tests.
- Stool tests, such as:
- A fecal immunochemical test (FIT).
- A fecal occult blood test (FOBT).
- Flexible sigmoidoscopy.
The method of screening that you have depends on your personal preferences, your doctor's preferences, and what the clinic or office you go to is able to do.
People with a higher risk for colon cancer, such as those with a strong family history of colon cancer, may need to be tested sooner. Talk to your doctor about when you should be tested.
If you have a family history of familial adenomatous polyposis (FAP), you should start screening tests at age 10 or 12.
If you have a family history of hereditary nonpolyposis colon cancer (HNPCC), you should have a colonoscopy every 1 to 2 years starting at age 20 to 25, or 10 years younger than the age at which the youngest family member who has colorectal cancer was diagnosed, whichever comes first.
Talk with your doctor. Decide with him or her when to start and stop screening for colon cancer. These decisions will depend on how old you are, your family history, any health problems you have, and the benefits you can expect from regular screening.
Most doctors agree that if you have had one or more adenomatous polyps removed, you probably need regular follow-up colonoscopy exams every few years. This type of polyp is more likely to turn into cancer, but that risk is still very low. How often you need a colonoscopy may depend on the number and size of the polyps, your age, your health, and other risk factors that you may have for polyps. Talk with your doctor about the follow-up testing schedule that is right for you.