Colorectal Cancer Screening Tests
Reviewed
Also called: Colon cancer screening, Colorectal cancer screening tests, Bowel cancer screening
Colorectal cancer screening tests check for colorectal cancer before you have any symptoms.
Specimen: Stool sample (for stool tests); not applicable for visual exams
Why this test may be ordered
- To check for signs of colorectal cancer before symptoms appear
- To find and remove colorectal polyps that could become cancerous
- Routine screening starting at age 45 for average-risk individuals
- Earlier or more frequent screening if you have risk factors such as family history, inflammatory bowel disease, or obesity
Preparation and collection
There are no special preparations needed for a FIT or stool DNA test. For a colonoscopy and virtual colonoscopy, you will need to do a bowel prep. Also, you may need to stop taking certain medicines before these tests, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.
There are two main types of colorectal cancer screening tests: visual exams and stool tests. Visual exams are procedures that allow your provider to look inside your colon and rectum. You will be given a medicine called a sedative to help you relax and prevent you from feeling pain during the procedure. The sedative may make you drowsy for several hours. You should arrange for someone to take you home.
There are no risks to having a fecal occult blood test or a stool DNA test. Serious risks of colonoscopy are rare but can include: Tears in the colon or rectum wall, Bleeding, Reaction to the sedative. Seek medical care immediately if you have severe abdominal pain, blood in your stool or bleeding from your anus, dizziness, or weakness.
Understanding results
Each type of screening test has advantages and disadvantages. You and your provider should discuss the benefits and risks of each option.
- Abnormal stool test (FIT or stool DNA): If your fecal occult blood test or stool DNA test had abnormal results, it doesn't necessarily mean you have cancer. Limitation: Can have false positives, which means your test results show that blood is in your stool, but there isn't any. Next step: But your provider will probably order more tests, such as a colonoscopy, to help make a diagnosis.
- Colonoscopy: polyps or abnormal tissue found and removed: Colorectal polyps or abnormal tissue were found and removed. Samples were sent to a lab for testing. Most polyps aren't cancerous but can turn into cancer if not removed. Limitation: Most polyps aren't cancer, but removing them can prevent them from becoming cancer later on. Next step: Depending on the size and number of polyps, your provider may recommend more frequent colonoscopies.
- Sigmoidoscopy: polyps or abnormal tissue found: Colorectal polyps or abnormal tissue were found. They may or may not be removed depending on their location. Limitation: Only looks at a third of the colon. Next step: Whether or not your polyps were removed, you will probably need a colonoscopy so your provider can view your entire colon and rectum.
- Virtual colonoscopy: polyps or abnormal tissue seen: Colorectal polyps or abnormal tissue were seen on the CT scan. Limitation: Polyps cannot be removed during the procedure. Next step: You may need a traditional colonoscopy so your provider can get a tissue sample.
- Stool tests can have false positives and may miss some polyps or cancers.
- Stool tests cannot detect precancerous changes.
- Visual exams may miss small polyps.
- Virtual colonoscopy cannot remove polyps; a traditional colonoscopy is needed if abnormal.
- Sigmoidoscopy only looks at the lower third of the colon.
What to do next
If you have questions about your results, talk to your provider.
- What type of colorectal cancer screening test is right for me?
- How often should I get screened?
- What are the benefits and risks of each screening option?
- Do I need to prepare for the test, and if so, how?
- What do my results mean and what are the next steps?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: Colorectal Cancer Screening Tests