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). This screening 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 before age 50.
If a large polyp or growth is found in your colon, you may need a standard colonoscopy to remove the polyp. “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. If you have the standard colonoscopy on the same day or next day, you do not need a second bowel prep.
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. Or, small polyps can be removed by standard colonoscopy, the same day or later, if you choose.
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 be 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 want to be able to have a same-day standard colonoscopy if a polyp is found, stop taking iron tablets five days before the exam. If you cannot have a standard colonoscopy the same day because you do not have a driver, are on blood thinners or anti-platelet medicines, or have other plans, you may keep 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, avoid foods that are digested slowly (corn, popcorn, potato skins, nuts, fruits with skin or seeds, uncooked or raw vegetables) because they may interfere with your prep.
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 some 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.
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, 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
Do not stop taking them unless your doctor tells you to. Some examples include:
Pradaxa ® (Dabigatran).
VC is often advised for patients taking these types of medicines. There is a greater risk to stopping blood thinners for a standard colonoscopy. VC can safely look at 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 and any special instructions to do so safely with the doctor who prescribed the medicine for you.
Only stop iron tablets 5 days before your VC exam, if you have been told to stop the blood thinner or anti-platelet medicine.
If you think you may be pregnant, do not start the prep kit; you cannot have a VC exam while pregnant. If you think 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. To get a clean and empty colon you will start to prepare the day before your exam. The bowel prep kit includes a laxative, contrast medicines and instructions for a clear liquid diet. The laxative helps clean out the bowel for the exam. The contrast agents help to highlight any stool or fluid left in your colon on the VC pictures.
Starting at midnight the entire day before your exam (prep day), drink as many clear liquids as you want. If you have to limit your fluid intake, speak with your doctor to make sure this prep is right for you. The GoLYTELY® described below does not count toward your fluid intake.
Drink only clear liquids for breakfast, lunch, dinner, and snacks. Do not eat any solid foods. Drink plenty of fluids to avoid dehydration. Avoid red or purple liquids (i.e., red Jell-O, cranberry juice, purple sports drinks). Clear liquids include:
Gatorade®, Powerade® (we suggest sports drinks with electrolytes to help with hydration)
Water, tea, or coffee without cream or milk (sugar or honey is okay)
Vitamin water®, Crystal Light®
Jell-O®, Popsicles® (no fruit or cream added)
Bouillon or broth (chicken, beef, or vegetable)
Apple, white cranberry, or white grape 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 ClearTM, or Resource® Breeze
How to Prepare GoLYTELY® Solution
Read the directions on the GoLYTELY® bottle. Add water to the “fill” mark on the bottle. Shake it until all the powder is dissolved. Do not add ice. Do not add any other liquids or flavors except, if desired, two packets of Crystal Light® yellow lemonade powder with Nutrasweet®. You may also try to flavor by the glass, instead of adding it to the entire bottle. You may drink the GoLYTELY® with no flavoring.
It may taste better if it is chilled. Put it in the fridge, but do not add ice. You are drinking a large amount of liquid quickly, you may become chilled. This is normal. It can help if you wear warm clothing, cover up with a blanket warmed in the dryer, or drink it at room temperature.
If you take other medicines, don’t take them while drinking GoLYTELY®. Take them at least 1 hour before starting GoLYTELY® or at least 1 hour after you are done drinking. If you need to limit your fluid intake, please note that the GoLYTELY® does not count towards your fluid intake. GoLYTELY® is not absorbed by your colon.
If you wish, you may put the GoLYTELY® and barium sulfate in the fridge. Or, you may drink them at room temperature. Do not put the Omnipaque (iohexol) in the fridge and do not store the bottle where it would be in direct sunlight.
Step 1 – At 8 AM or before: Take the four Bisacodyl® tablets (5 mg each) with 1 glass (8 ounces) of clear liquid. Do not chew or crush them. Do not take them within 1 hour of taking an antacid. This will gently move your bowels to help the GoLYTELY® work better. You can take these tablets and still do normal activities because they rarely cause diarrhea.
Step 2 – Start anytime between 12 Noon and 2 PM: Prepare the entire bottle of GoLYTELY®. It may take some people longer to drink GoLYTELY®, so adjust the start time based on how well you think you will be able to tolerate the prep. You should try to be cleaned out of stool by about 6 pm.
• Drink with a straw to lessen the taste.
• Try gum or clear hard candy between glasses.
• For a sore bottom after a bowel movement, cleanse with baby wipes and apply a protective ointment such as A+D® or Vaseline®. TUCKS® medicated cooling pads may also provide relief.
Drink one 8-ounce glass every 10 minutes. If you feel sick to your stomach, stop drinking until the nausea passes. Begin to drink again, but at a slower rate (one 8-ounce glass every 15-20 minutes).
About one hour after you start to drink the GoLYTELY® you will likely begin to have diarrhea. Stay close to a bathroom. You may have some cramping in your lower abdomen. This is normal. If you start to have severe, steady stomach pain, get dizzy, or you don’t expel any of the GoLYTELY®, call your primary care doctor.
When you have finished half of the bottle of GoLYTELY®, you may stop if your bowel
movements are watery and free of solids (flecks are OK). The color may be clear to yellow, green, or tan, but must be see-through.
If your bowel movements are not as described, keep drinking the GoLYTELY® until you feel your bowels are cleaned out. Most people will only need to drink half of the GoLYTELY®. Others may need to drink the entire bottle to clean out the colon and get the best exam.
If You Finish the GoLYTELY® by 6 PM
Step 3 – At 7 PM: 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 CT images. There is no lactose in the barium. You may keep drinking clear liquids as desired.
Step 4 – At 9 PM: Omnipaque (iohexol) is another contrast medicine that helps highlight fluid in your colon. The bottle says it is for “injection,” but this medicine can also be taken by mouth. 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 then follow it with 8 ounces of clear juice, water, or soda. You do not need to drink it quickly.
If You Cannot Complete the Time Schedule
• If at 6 pm you still have more GoLYTELY® to drink and are not cleaned out of stool, keep drinking it.
• One hour after you’re finished, drink the barium sulfate (Step 3).
• Two hours after that, drink the Omnipaque (iohexol) (Step 4).
Your bowel prep is done!
You may keep drinking clear liquids until midnight.
The 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 when you can’t eat as well as before your exam. You should adjust your insulin or oral diabetes pills 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. 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.
You do not need to have anyone 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 where you will lie on the CT exam table.
A small tube is gently placed a very short distance into your rectum. Carbon dioxide is placed slowly into your colon. The exam should not be painful, though you may have some abdominal 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 of your abdomen and pelvis 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
To find out more about the virtual colonoscopy exam and prep, please see our video at https://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 doctor’s on call service. If your referring doctor is from outside the UW Health system, you may call the paging operator for urgent VC concerns at 608-263-6400 and ask for the radiology resident on-call.
If you need urgent medical help, call 911 or go to the nearest emergency room.
If you need to reschedule for any reason, call 608-263-9729.
The Spanish version of this Health Fact for You is #6293s.