Colorectal Cancer Screening Tests
Reviewed
Colorectal cancer screening tests check for colorectal cancer before you have any symptoms. They can find cancer early, when treatment is most effective, and help prevent cancer by finding and removing abnormal growths called polyps.
Preparation and collection
Preparation depends on the test type. For colonoscopy and virtual colonoscopy, you need bowel prep: follow a liquid diet for 1-3 days, drink clear liquids, and take a strong laxative or enema. For sigmoidoscopy, you may need a clear liquid diet, fasting, and an enema. For gFOBT, avoid NSAIDs, vitamin C, certain vegetables, and red meat for several days. No special preparation is needed for FIT or stool DNA tests.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- 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
Discuss your results with your healthcare provider to determine the best follow-up plan. If your test was abnormal, you may need a colonoscopy for further evaluation. If your test was normal, continue with routine screening as recommended.
Evidence source
U.S. National Library of Medicine: Colorectal Cancer Screening Tests