Colon Cancer Screening: What It Is and What to Expect
Medically reviewed by Achuta Uppu, MD, Internal Medicine. Last reviewed: October 23, 2026.
What kind of doctor provides Colon Cancer Screening?
A gastroenterologist, a doctor who treats the digestive system, usually performs colonoscopy and sigmoidoscopy, which are scope exams of the colon. Your regular doctor can order stool tests, which are done at home. A direct primary care or concierge doctor can be a first stop for an evaluation and can refer you to a specialist when needed.
What it is
Colon cancer screening checks for colorectal cancer before you have any symptoms. Colorectal cancer is cancer of the colon or rectum. Polyps, which are abnormal growths in the colon, can turn into cancer. Screening can find polyps so they can be removed first. It can also find cancer early, when treatment works best.
Why a doctor might recommend it
The U.S. Preventive Services Task Force recommends screening for adults age 45 to 75. For ages 76 to 85, the choice is made person by person. You may need to start earlier, or be screened more often, if you have inflammatory bowel disease (such as Crohn's disease or ulcerative colitis), a personal or family history of colorectal cancer or polyps, or a genetic syndrome such as Lynch syndrome. Ask your doctor which test is right for you.
How to prepare
Stool tests need no special preparation. A colonoscopy, a virtual colonoscopy, and a sigmoidoscopy need a bowel prep, which clears stool from your colon so the doctor can see it. Steps may include the following.
- Follow a liquid diet for one to three days before the test.
- Avoid red or purple drinks and gelatin, because the dye can look like blood in the colon.
- Take a laxative, a medicine that causes a bowel movement, as directed. Stay close to a bathroom.
Tell your provider about everything you take. Do not stop any medicine unless your provider tells you to. For a colonoscopy, plan a ride home.
What happens during it
For a colonoscopy, you get sedatives or anesthesia through an IV, so you do not feel pain. The doctor guides a long, thin, lighted tube with a camera through your rectum and the whole colon. The doctor can find and remove most polyps and some cancers. It usually takes less than one hour.
A sigmoidoscopy checks only the rectum and the lower third of the colon. A virtual colonoscopy uses X-rays and a computer to picture the whole colon and needs no sedative. For a stool test, you collect a sample at home and send it to a lab.
Recovery
After a colonoscopy, you stay about 30 to 60 minutes while the sedatives wear off. You may have cramping or bloating during the first hour. You should expect a full recovery and a normal diet by the next day. Light bleeding from your anus is normal if the doctor removed polyps or took a biopsy, a small tissue sample.
If a stool test, sigmoidoscopy, or virtual colonoscopy is abnormal, a colonoscopy is needed to finish the screening.
Risks and side effects
Stool tests have no risk to the colon. Serious risks of colonoscopy are rare. They include bleeding, a tear in the colon wall, and a reaction to the sedative. Bleeding can also happen up to 2 weeks later. A sigmoidoscopy has fewer risks. A virtual colonoscopy uses a small dose of radiation and is not recommended in pregnancy.
An abnormal stool test result does not necessarily mean you have cancer.
Call 911 or go to the emergency room if bleeding from your anus will not stop, or if you have severe belly pain, sudden dizziness or weakness, fainting, or trouble breathing.
Who performs it
A doctor performs a colonoscopy at a hospital or an outpatient center. A virtual colonoscopy is usually done in the radiology department. Your provider usually prescribes a stool test, and you do it at home.
Common questions
How often do I need colon cancer screening?
It depends on the test. For people at average risk, a FIT stool test is done once a year, a stool DNA test every 3 years, a sigmoidoscopy every 5 years, a virtual colonoscopy every 5 years, and a colonoscopy every 10 years.
What if my stool test is abnormal?
An abnormal stool test does not necessarily mean you have cancer. Your provider will probably order more tests, such as a colonoscopy, to find the cause.
How does a direct primary care or concierge doctor fit in?
A direct primary care doctor charges a flat monthly fee instead of billing insurance, while a concierge doctor usually charges more and often works alongside insurance. Either one can help you choose a test, order stool tests, and refer you to a specialist for a colonoscopy.
Sources
- MedlinePlus - Colorectal Cancer Screening Tests
- Centers for Disease Control and Prevention - Screening for Colorectal Cancer
- National Institute of Diabetes and Digestive and Kidney Diseases - Colonoscopy
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
