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Getting ready for a virtual colonoscopy (CT colonography): why, the prep, the day of, and after
For anyone who has a virtual colonoscopy coming up, or who is helping someone through one. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK, part of the NIH) says virtual colonoscopy, also called CT colonography, is a procedure in which a radiologist uses images created by x-rays and a computer to examine your rectum and colon from outside the body, and that doctors mainly use it to screen for colon polyps and colorectal cancer. This page passes on, by name, what NIDDK says: why doctors use it and how it differs from a colonoscopy; your health, your medicines and the special diet; the bowel prep and the contrast medium; what happens during the procedure; and the report, the risks, and when to get care right away. It builds the words to say and the questions to ask, and prints a card for the fridge.
Right now
- Trouble breathing, chest pain, fainting, or heavy bleeding with dizziness? Call 911 (ours).
- After a virtual colonoscopy: severe pain in your belly, fever, bloody bowel movements, bleeding from the anus, dizziness, or weakness? NIDDK says to seek care right away.
- Side effects keep you from finishing the bowel prep? NIDDK says to call a health care professional.
- Allergic to contrast medium, have an implanted medical device, or are or may be pregnant? NIDDK says to tell your doctor before the procedure.
- Not sure whether to stop a medicine before it? Ask the doctor who ordered the procedure. Do not stop or change a prescribed medicine on your own (ours).
- It is all too much, or you are thinking of ending your life? Call or text 988, any hour (ours).
More help
- The belly, on this site: Getting ready for a colonoscopy · Getting ready for a flexible sigmoidoscopy · Colon polyps · Bleeding in the digestive tract · Ulcerative colitis · Crohn’s disease · An upset stomach: find the right page.
- Getting there and getting ready: Rides to care · My medicines list · Symptom diary · Get ready for your appointment.
- If the news is hard: When the doctor says cancer.
- Care and costs: When you need a doctor and can’t pay · Medical bills.
- In a crisis: Help right now (988, 911). All our free tools.
An upset stomach, and not sure this is the right page? The pages on this site for throwing up, diarrhea, heartburn and constipation, on one list.
This page and its wording were written with AI (Claude) for Scarlet Beast (our AI policy). No doctor or nurse has reviewed it. The facts were read on October 17, 2026 on NIDDK’s Virtual Colonoscopy page (NIH) and its Spanish version, both last reviewed in July 2024 and saying the same things; the cards also point to NIDDK’s Colonoscopy, Flexible Sigmoidoscopy and Colon Polyps pages. The numbers (screening usually from age 45; older than 75, talk with your doctor; about 15 minutes; cramping or bloating for up to 24 hours) are NIDDK’s. NIDDK gives no number for the risk of perforation, only that it is very low, and none for radiation, so neither do we. Ours: 911 for trouble breathing, chest pain, fainting, or heavy bleeding with dizziness; asking ahead which medicines change, and never stopping one on your own; writing down when the clear liquids start and stop and when to take the prep and the contrast medium; mentioning a past reaction to contrast medium when you book; telling the team you are nervous; asking who tells you the results, whether a colonoscopy comes next, and why any extra test is suggested; the card; 988 when it is too much; health centers when money is tight; and the order of the steps. What we left out: laxative, enema, contrast medium and sedative names, brands, doses, and clinical pages for providers. This page saves nothing and loads no trackers.