A colonoscopy is an exam of the rectum and the entire colon, or large intestine. Your gastroenterologist uses a colonoscope, a thin and flexible tube with a light and a camera, to inspect the lining of the colon on a video monitor.
It is the one screening test that can both find and fix: if polyps are discovered, they are usually removed during the very same exam, before they have a chance to turn into cancer.
Why your gastroenterologist recommends it
The most common reason is colorectal cancer screening. Most colorectal cancers begin as polyps, and removing polyps early is the best protection available.
Colonoscopy is also used to investigate symptoms such as bleeding, a lasting change in bowel habits, chronic diarrhea, unexplained anemia, or abdominal pain, and to keep watch after previous polyps or in conditions such as inflammatory bowel disease.
Preparing for the exam
The colon must be completely clean for your doctor to see small polyps. Starting a few days before, you may be asked to avoid certain high-fiber foods; the day before, you will switch to clear liquids and take your prescribed prep, usually split into an evening dose and an early-morning dose.
The prep causes frequent, watery bowel movements — that means it is working. Follow every step of your instructions, and arrange for someone to drive you home.
During the procedure
Sedation is given through a small IV, and most patients sleep comfortably and feel little or nothing. While you rest on your side, the doctor guides the colonoscope through the colon and examines the lining carefully.
Removing polyps and taking biopsies are painless. The exam itself typically takes well under an hour.
Afterward and your results
You will wake in a recovery area and may feel gassy or bloated for a short while as the air used during the exam passes. Most people eat normally later the same day and return to their usual activities the next morning.
Your doctor will usually explain what was found before you go home; biopsy results follow within days. How soon you need another colonoscopy depends on what was found, and your care team will give you a clear timeline.
Questions about your care?
This page is general education, not personal medical advice. Your care team is happy to talk through what it means for you.
Preparing for a procedure? See preparation instructions