Virtual colonoscopy is used to check for colon cancer in people who are at least 45 years old.

A healthcare professional may suggest a virtual colonoscopy if you:

• Are at an average risk of colon cancer.
• Do not want medicine that puts you to sleep.
• Need to drive after the test.
• Don't want to have a colonoscopy.
• Are at risk of colonoscopy side effects, such as a lot of bleeding because your blood doesn't clot in the usual way.
• Have a bowel blockage.

You aren't able to have a virtual colonoscopy if you have:

• A history of colon cancer or unusual tissue clumps called polyps in your colon.
• A family history of colon cancer or colon polyps.
• Inflammatory bowel disease, such as Crohn's disease or ulcerative colitis.
• Acute diverticulitis.

Studies have shown that virtual colonoscopy finds large polyps and cancer at about the same rate as does traditional colonoscopy.

Because virtual colonoscopy looks at the entire abdomen and pelvic area, many other diseases may be found. Conditions unrelated to colon cancer, such as changes in the kidneys, liver or pancreas, can be detected. This may lead to more testing.

Virtual colonoscopy is generally safe. Risks include:

• A tear, also called a perforation, in the colon or rectum. The colon and rectum are filled with air or carbon dioxide during the test and this carries a small risk of causing a tear. However, this risk is lower compared with that of traditional colonoscopy.
• Exposure to a low level of radiation. Virtual colonoscopy uses a small amount of radiation to make the pictures of the colon and rectum. Healthcare professionals use the lowest amount of radiation possible to take a clear picture. This is about the same as the amount of natural radiation you might be exposed to in two years, and much less than the amount used for a regular CT scan.

Not all health insurance providers pay for virtual colonoscopy for colon cancer screening. Check with your health insurance provider to see which tests are covered.

Before the test

Before a virtual colonoscopy, you'll need to empty your colon. Any stool left in the colon may cloud the pictures taken during the exam.

To empty your colon, carefully follow the instructions from your healthcare team. You may be asked to:

• Follow a special diet the day before the exam. Typically, you won't be able to eat that day. Drinks may be limited to clear liquids. You may not be able to eat or drink anything after midnight the night before the exam.
• Take a laxative the night before the exam. You also may need to use a suppository to clear any remaining stool in your colon.
• Take medicine to identify stool in your colon. The medicine helps the healthcare professional see the difference between stool and changes in the colon.
• Adjust your usual medicines. Remind your health professional about your medicines at least a week before the exam. You may need to stop taking certain medicines days or hours before the exam.

During the test

You wear a gown but likely no other clothes. Medicine that makes you sleep during the test usually isn't necessary, but you may be given medicine to relax your colon.

You begin the exam lying on your side on the exam table, usually with your knees drawn toward your chest. A nurse or technologist places a small tube called a catheter inside your rectum. Through this catheter, your colon is filled with air or carbon dioxide as you roll over on the table while keeping your spine straight. The air or gas helps create clear pictures and may cause a feeling of pressure in your stomach area.

For the next part of the exam, you lie on your back. The exam table moves into the CT machine, which scans your body. Then you turn over to lie on your belly or your side and your body is scanned again.

You may be asked to turn and hold some other positions as well as hold your breath at times.

A virtual colonoscopy typically takes about 15 minutes.

After the test

You can go back to your usual activities after your virtual colonoscopy. You may feel bloated or pass gas for a few hours after the exam as you clear any remaining air or gas from your colon.

A healthcare professional will go over the results of the colonoscopy and then share them with you.

Your test results may be:

• Negative. This is when the test finds no changes in the colon. If you're at average risk of colon cancer and you have no colon cancer risk factors other than age, your health professional may suggest repeating the exam in five years.
• Positive. This is when the pictures show polyps or other changes in the colon. For positive results, your health professional will likely suggest a traditional colonoscopy to get samples of tissue or remove the polyps. Sometimes, the traditional colonoscopy or polyp removal can be done the same day as the virtual colonoscopy.
• Finding other changes. With this result, the imaging test finds changes outside the colon, such as in the kidneys, liver or pancreas. These findings may or may not be important, but you may need more testing to find their cause.