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Getting Ready for Your Virtual Colonoscopy (VC) (Routine VC Prep)

What is virtual colonoscopy?

Virtual colonoscopy (VC), also referred to as CT colonography, is a less-invasive, safe exam used for colon polyp screening. The entire colon lining can be seen with VC. A computed tomography (CT) scan creates a 3-D picture of the inside of your colon. This helps the doctor look inside the colon without having to insert a scope.

The main purpose of this exam is to screen for growths (polyps) in the lining of the large intestine (colon and rectum). Screening for colorectal cancer and colon polyps should start at age 50. If you have a first-degree relative (a parent, brother, sister, or child) with colorectal cancer, your doctor may decide to start screening earlier than age 50.

If a large polyp or growth is found, a standard colonoscopy may be needed to remove it. “Large” polyps are those 1 cm (about ⅜ inch) or greater. They are removed because they have a higher chance of turning into cancer. A growth of this size is present in less than 5% of all patients. A nurse will set up the standard colonoscopy, if needed. If this occurs, someone needs to drive you home. Scheduling the standard colonoscopy on the same day or next day means a second bowel prep is not needed.

Doctors at UW Health can also watch a small colon polyp over time. Smaller polyps, 6 mm to 9 mm (about ⅓-¼ inch), can be safely watched by having a follow up VC exam in 3 years. But small polyps can also be removed by standard colonoscopy, the same day or later, if you would like.

VC also allows the doctor to take a limited look outside the colon for problems in the abdomen and pelvis. This may help find problems, such as abdominal aneurysms, other cancers, or conditions you may not have been aware of. At many locations where VC is done, we may also be able to do a CT BMD (bone mineral density) exam to screen for osteoporosis. It is done at the same time as your VC exam with no extra scans or cost.

Getting Ready for Your VC Exam

If you would like to have a same-day standard colonoscopy if a polyp is found, stop taking iron tablets five days before the exam. If you are not able to have a standard colonoscopy the same day, you may continue taking iron tablets. Iron tablets do not affect the VC exam. If you have any questions or concerns about stopping a medicine, call your doctor. You may take all other prescribed medicines before your VC.

Three days before the exam, try to avoid foods that are digested slowly (corn, popcorn, potato skins, nuts, fruits with skin or seeds, uncooked or raw vegetables), they may interfere with your prep.

Changes If You Have Diabetes

Call your doctor to discuss how your diabetes medicine should change before the VC. Test your blood sugar more often the day before this test. Also check your blood sugar the morning of your test. If your blood sugar level is low (less than 70 mg/dL) or if you have symptoms, take glucose tablets or drink 4 ounces of a clear liquid that contains sugar. Always recheck your blood sugar level to make sure it stays above 70 mg/dL.

We can still do the VC unless you need to eat solid food to keep your blood sugar at a normal level. If the blood sugar ever gets too high or too low and you can’t bring it back to normal, call your primary care or diabetes doctor.


If you get diverticulitis before your VC exam, call your doctor first. Then contact the VC office to reschedule your exam for at least four weeks after your treatment.

Blood Thinners or Anti-Platelet Medicines

If you take blood thinners or anti-platelet medicines, do not stop taking them unless your doctor tells you to.
Some examples include:

  • Coumadin® (warfarin),

  • Plavix® (clopidogrel),

  • Effient® (prasugrel), and

  • Pradaxa® (Dabigatran).

VC is often advised for patients taking these medicines. There is a greater risk to stop blood thinners for a standard colonoscopy. VC can safely evaluate your colon without stopping these medicines. If a polyp is found that should be removed, we will consult with your doctor who can set up the standard colonoscopy at a later date.

If your doctor tells you to stop these medicines so that you can have a same-day standard colonoscopy if a polyp is found, you must discuss how long to stop the medicine for and any special instructions to do so safely with the doctor who prescribed the medicine for you.

If you take iron tablets, stop taking them 5 days before your VC exam, but only if you have been told to stop your blood thinner or anti-platelet medicine. Otherwise you may keep taking iron.


If you think you may be pregnant, do not start the prep kit; you cannot have a VC exam while pregnant. If you are concerned that you could be pregnant, call the VC office. A pregnancy test will be ordered before starting the prep.

The Day Before Your Exam (“Prep Day”)

Proper bowel cleaning is needed for the best exam. This starts the day before your exam with a clear liquid diet, laxatives and contrast medicines. The laxative helps clean out the bowel. The contrast helps to show any stool or fluid left in your colon on the VC pictures.

Starting at midnight the day before your exam (prep day), drink as many clear liquids as you want. If you are on a fluid restriction, speak with your doctor to make sure this prep is right for you.

Drink only clear liquids for breakfast, lunch, dinner, and snacks. Do not eat any solid foods. Drink plenty of fluid to avoid dehydration and make the laxative work better. Avoid red or purple liquids (such as red Jell-O, cranberry juice, purple sports drinks, etc.). Clear liquids include:

  • Gatorade, Powerade (sports drinks with electrolytes)

  • Water, tea, or coffee (no cream or milk; sugar or honey is okay to add)

  • Vitamin water, Crystal Light

  • Bouillon or broth (chicken, beef, or vegetable)

  • Jell-O, popsicles (no fruit or cream added)

  • Apple, white grape, or white cranberry juice (no orange, tomato, grapefruit, or prune juice)

  • Soda such as Sprite, 7-Up, ginger ale, Mountain Dew, or colas

  • Clear hard candy, gum

  • Lemonade (with no pulp), iced tea

  • Clear liquid protein drinks such as Ensure Clear TM, or Resource Breeze

Bowel Prep Medicine Schedule

If you take other medicines, take them at least one hour before or at least one hour after taking the laxative (magnesium citrate). You may put the magnesium citrate and barium sulfate in the refrigerator or you may drink them at room temperature. Do not put the Omnipaque (iohexol) in the refrigerator and do not store the bottle where it would be in direct sunlight.

You may have as many clear liquids as you like between each step and up until midnight.

Step 1 – Anytime in the morning before 11AM. Take the two Bisacodyl tablets (5 mg each) with 1 glass (8 ounces) of clear liquids. Do not chew or crush them. Do not take them within 1 hour of taking an antacid. This will gently move your bowels (6-8 hours after you take this medicine) to help the laxative taken in Step 2 work better. You can take these tablets and still do normal activities because they rarely cause diarrhea.

Helpful Hints

  • Drink with a straw to lessen the taste.

  • For a sore bottom after a bowel movement, cleanse with baby wipes. Apply a protective ointment such as A+D®, or Vaseline®. Try TUCKS® medicated cooling pads to provide relief.

Step 2 – Begin this step anytime between 2 and 6 PM. The later you start the laxative, the later you may be up having bowel movements. Drink one bottle (296 mL) of magnesium citrate. Follow this with at least 4 to 6 cups of clear liquids before Step 3. This is a laxative, so you should begin to have closely spaced bowel movements. You will want to be near a bathroom. The time it takes for the laxative to start working varies for each person. Wait at least 2 to 3 hours from the time you took the first bottle of magnesium citrate before going on to Step 3.

Step 3 – Between 4 and 9 PM. There should be 2-3 hours between drinking the first bottle of magnesium citrate and the start of Step 3.

  • Drink the entire 225 mL bottle of liquid barium sulfate suspension found in the prep kit. This is a contrast medicine used to highlight any leftover stool on the VC pictures. There is no lactose in the barium.

  • Drink the second bottle (296 mL) of magnesium citrate. This is a laxative and will continue the process of cleaning out the colon. Follow this with at least 4 to 6 cups of clear liquids before Step 4. You can drink the 4 to 6 cups of clear liquids quickly, or you can stretch the clear liquids out over the next 2 to 3 hours if you are feeling full.

Step 4 – Between 6 and 11 PM. Step 4 should begin 2-3 hours after drinking the second bottle of magnesium citrate.
Omnipaque (iohexol) is another contrast medicine that helps highlight fluid in your colon. The bottle says it is for “injection,” but you can drink it. We want you to drink this medicine so that it will be in your colon by the next morning for your exam.

The plastic bottle has a pull-tab on the top, but you do not need to pull this. Instead, twist the entire top to remove it. Also remove the black rubber stopper before drinking the contrast.

Drink the entire 50 mL bottle of Omnipaque (iohexol) 350 mgI/mL. You may mix it in 8 ounces of clear juice, water, or soda and drink. Or, drink the Omnipaque and follow it with 8 ounces of clear juice, water, or soda. You do not need to drink it quickly.

Your bowel prep is done!

You may keep drinking clear liquids until midnight.

Day of Your Exam
Do not eat or drink anything after midnight
the day of your exam until you are told to do so after your exam. You may take your daily medicines as prescribed with small sips of water. If you haven’t been able to have a bowel movement or to finish the prep kit, call the VC office to ask if the exam can still be performed or if we need to set up for a later date.

If you have diabetes, test your blood glucose level more often before your exam. You should adjust your insulin or other diabetes medicines as discussed with your doctor. Go back to your normal schedule after you get the exam results and can eat again. If your blood glucose level is low (less than 70 mg/dL) or you have symptoms, please drink a clear liquid that has sugar in it or take glucose tablets. Always recheck your blood sugar level to make sure it stays above 70 mg/mL. We can still do the exam unless you need to eat solid food to maintain your blood glucose. It is better to maintain your blood glucose than to have the exam. We can always schedule your VC in the future.

Driving Home
You do not need to have someone drive you to and from the VC exam. You are not given any medicine that will make you sleepy. If you need a standard colonoscopy the same day, you will need to arrange for someone to drive you for that test.

During the Exam

The VC exam takes about 30 minutes or less. Allow up to 50 minutes to change your clothes and talk with the CT technologist (tech). You do not need pain or sedation medicine or an IV for this exam. You will change into a hospital gown and then go to a CT exam room. Staff will help you lie down on the exam table.

A small tube is gently placed a very short distance into your rectum. Carbon dioxide will be placed slowly into your colon. The exam should not be painful, though you may have some belly fullness, discomfort, or cramping. You may feel the urge to have a bowel movement. These feelings should go away as soon as the exam is over.

Pictures are taken while you are lying on your back and then on your stomach. If you are unable to lie on your stomach, we can take pictures while lying on your side. You are asked to hold your breath for about 10 seconds while the CT scanner takes pictures.

After the Exam

The CT tech will ask you for your phone number so the team can call you with your colon results in about 2 hours. Many people go back to work or other activities after the exam.

  • If you wish to have a polyp removed the same day as your VC, please do not eat or drink until you hear from us. If you need to have a standard colonoscopy, the VC team can set up this second exam for the same day as long as you have not eaten or had liquids to drink.

  • If you take prescription blood thinners, anti-platelet medicines, or do not wish to have a same-day
    standard colonoscopy, you may go back to your normal diet right after the exam. If a polyp is found that should be removed, a standard colonoscopy is set up at a later date by your doctor’s office.

  • If you do not have colon polyps, you can go back to your normal diet and any medicines you may have stopped when we call with the results. If you have colon polyps, we will review options with you and help set up further care as needed.
    If any other problems are seen outside your colon, the results are sent to your doctor in the full VC report. If you have not heard from your doctor about other results within 2 weeks, we suggest you call your doctor’s office to follow up.

Who to Call

For more information on the virtual colonoscopy exam and prep, please see our video at uwhealth.org/vcprep

VC Program Office to speak to a nurse or team member: 608-263-9630

If you have an urgent concern after normal business hours, contact your primary care doctors on-call service. If your referring doctor is from outside the UW Health system, you may call the paging operator for urgent VC related concerns at 608-263-6400 and ask for the radiology resident on-call.

If you need immediate medical help, call 911 or go to the nearest Emergency Room.

If you need to reschedule for any reason, please call Radiology Scheduling at 608-263-9729.