This information will help you get ready for your virtual colonoscopy at Memorial Sloan Kettering (MSK) if you have an allergy to iodinated or CT contrast.Back to top
About Your Virtual Colonoscopy
A virtual colonoscopy (VC), also known as a computed tomography (CT) colonography is done to take pictures of your colon (large intestine) and rectum (the last part of your colon) to look for signs of cancer. Adults ages 50 years and over should be screened for colon polyps. Colon polyps are growths attached to the inner wall of your colon. They are usually benign (not cancerous), although some can be cancerous or precancerous.
During your VC, your technologist will use a CT scan to take 3-D pictures of the inside of your colon and rectum. A VC is different from a regular colonoscopy because your doctor can look at the inside of your colon without using a colonoscope (flexible tube placed in the rectum during a colonoscopy).
Your doctor will use the 3-D pictures to:
- Look for signs of colorectal cancer
- Look for growths (polyps) in your colon and rectum
Before Your Procedure
Pick up your prep kit
Before your VC, you’ll need to clean out (empty) your colon. To do this, you will need to pick up the following supplies from an MSK pharmacy:
- 2 (5 milligram) tablets of bisacodyl (Dulcolax®). You will get a box of 10 tablets, but you will only need to take 2.
- 2 (296 milliliter) bottles of magnesium citrate. This is a laxative that will clean out your colon.
- You can keep the magnesium citrate in the refrigerator or at room temperature.
You will also need:
- 64 ounces of any clear liquid that isn’t red, purple, or orange.
- We recommend that you get a sports drink like Gatorade® or Powerade®.
- If you have diabetes, be sure to get sugar-free clear liquids.
You may also need to pick up premedication for your VC prep. If your doctor told you that you will need to take contrast dye premedication for your VC, make sure you pick up your premedication at the pharmacy when you pick up the prep kit.
Ask about your medications
You may need to change the time you take your regular medications so it’s not at the same time as the medication needed for your bowel preparation. If you usually take your medications at the time you’re supposed to take one of your bowel preparation medications, plan to take your other medications 1 hour before or 1 hour after. If you’re having trouble planning your medication time, call your doctor or nurse.
If you take medication to thin your blood, such as to treat blood clots, do not stop taking it unless your doctor tells you to stop. Some examples of blood thinners include warfarin (Coumadin®), dalteparin (Fragmin®), dabigatran (Pradaxa®), enoxaparin (Lovenox®), clopidogrel (Plavix®), prasugrel (Effient®) and cilostazol (Pletal®). There are others, so check with your doctor if you aren’t sure.
Contrast is a special dye that makes it easier for your doctor to see abnormalities in your body. Oral contrast dye can be a medication given during bowel preparation for a VC but, because you’ve had a reaction to iodinated or CT contrast dye in the past, you will not use oral contrast dye during your preparation.
For people who take premedication
You still may get intravenous (IV) contrast dye for your VC. Call your doctor to find out if you will be getting IV contrast, if you haven’t talked about it already.
If you’re getting IV contrast and you usually take premedication, you will need to take premedication before your VC. Call your doctor if you have any questions.
For people with diabetes
- If you take insulin or other medications for diabetes, you may need to change the dose. Ask the doctor who prescribes your diabetes medication what you should do the day before and the morning of your procedure. Tell your doctor you will be drinking a clear liquid diet the day before your procedure.
- If you monitor your blood sugar (glucose) level, ask your doctor if you should stay on the same monitoring schedule. Call your doctor if your blood sugar falls below 70.
3 Days Before Your Procedure
Avoid certain foods
Don’t eat foods that are hard to digest. Food may make it difficult to see your organs in the pictures taken during your VC. If this happens, you may need to repeat the procedure.
Examples of foods that are hard to digest are:
- Raw fruits and vegetables. You can have vegetables that are cooked or canned.
- Whole kernel corn, including canned corn
- Potato skins
- Whole grains (such as oatmeal, brown rice, quinoa, or wheat bread)
- Seeds (such as poppy or sesame)
The Day Before Your Procedure
Begin your bowel preparation
During your bowel preparation, you’ll take laxatives and contrast medication. Be sure to follow these instructions carefully. It’s very important that your colon is empty for your VC. If your colon isn’t empty, it will be difficult to see polyps or other problems inside your colon. If this happens, you may need to repeat the procedure.
If you have any questions, call your doctor’s office.
Follow a clear liquid diet
You will need to follow a clear liquid diet the day before your procedure. Examples of clear liquids are listed in the table below. While you’re following the clear liquid diet:
- Don’t eat any solid foods.
- Don’t drink anything red, purple, or orange.
- Make sure to drink plenty of liquids in addition to water, coffee, and tea. Try to drink at least 1 (8-ounce) glass every hour while you’re awake.
You can drink as many clear liquids as you like between each step of your bowel preparation. Stop drinking clear liquids at midnight.
|Drink||Do Not Drink|
Follow your bowel prep medication schedule
The day before your VC, you will begin taking your bowel preparation medication. Follow the medication schedule in this section.
You may need to change the time you take your regular medications so it’s not at the same time as the medication needed for your bowel prep. If you usually take your medications at the time you’re supposed to take one of your bowel prep medications, plan to take your other medications 1 hour before or 1 hour after. If you’re having troubling planning your medication time, call your doctor or nurse.
Bowel prep schedule
Use the table at the end of this resource to write down the time you take each medication. If your doctor would like you to take your contrast dye premedication, you will need to plan when you will take your premedications as well. If you need help planning this, talk with your doctor or nurse.
Remember that you can drink clear liquids between each of these steps. Stop drinking clear liquids at midnight.
Step 1: Bisacodyl tablets
Anytime in the morning before 11:00 am, take 2 (5 milligram) bisacodyl tablets.
- Take them with 1 (8-ounce) glass of clear liquids.
- Don’t chew or crush them.
- Don’t take them within 1 hour of taking an antacid (medication to relieve heartburn or stomach pain), including calcium carbonates (such as Tums®) and histamine-2 blockers (such as Zantac®). Ask your doctor for more information.
The bisacodyl tablets will cause you to have a bowel movement about 6 to 8 hours after you take them. This will help the laxative taken in Step 2 work better. You can take these tablets and still do normal activities because they will rarely cause diarrhea (loose or watery bowel movements).
Step 2: First bottle of magnesium citrate
Between 4:00 pm, drink the first bottle of magnesium citrate.
- You may want to drink it with a straw to lessen the taste.
- This is a laxative, so you should begin having bowel movements more frequently. Your stool will become more and more loose and clear as you continue with your bowel prep. You will want to be near a bathroom. The time it takes for the laxative to start working varies for each person.
- If you don’t start having bowel movements within 2 hours after completing Step 2, call your doctor.
- Apply petroleum jelly (Vaseline®) or A & D® ointment to the skin around your rectum after every bowel movement. This helps prevent irritation.
Drink at least 4 to 6 cups (32 to 48 ounces) of clear liquids over the next 2 hours.
Step 3: Second bottle of magnesium citrate
At 6:00 pm, drink the second bottle of magnesium citrate.
Drink at least 4 to 6 cups (32 to 48 ounces) of clear liquids over the next 2 hours.
Now your stool should be more liquidy and yellowish-clear. This is a sign that your bowels are getting cleared. If your bowels aren’t getting cleared, call 212-639-7280 and ask to talk with a nurse or the fellow on call.
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Do not eat or drink anything after midnight except for your medications with a small sip of water.
The Day of Your Procedure
You may take your usual daily medications as prescribed with small sips of water.
What to expect
Once you arrive at the hospital, nurses, and other staff members will ask you to state and spell your name and date of birth many times. This is for your safety. People with the same or similar names may be having procedures on the same day.
When it’s time to change for your procedure, you will be asked to change into a hospital gown.
You will be taken into the CT exam room where you will lie on the CT exam table. A small tube will be gently placed into your rectum and secured to your leg or buttocks. It will feel like you’re having a rectal exam. The tube will inflate your colon with air or gas so that your technologist can get a better view. To help move the air or gas throughout your colon, you will be asked to change positions frequently. You will lie on your side, back, and abdomen (belly).
The VC isn’t painful, but you may feel some bloating, discomfort, or cramping. You may also feel like you’re going to have a bowel movement. These feelings should go away after your procedure.
You will be asked to hold your breath for about 10 seconds while the CT scanner takes pictures. Your technologist will take pictures of your abdomen and pelvis in at least 2 different positions (usually while you’re on your back and stomach).Back to top
After Your Procedure
- You may resume your normal diet after your VC.
- You may feel some cramping in your stomach after your VC. This is because of the gas used during your procedure. Walking can help relieve gas and reduce your cramping.
- It usually takes 2 to 3 business days to get your results. The doctor who sent you for your VC will call you when your results are ready.
Call Your Doctor or Nurse if You Have:
- A fever of 101° F (38.4° C) or higher
- Stomach pain, other than mild cramping
- Bleeding from your rectum, although a small amount of blood on toilet paper is normal 24 hours following your VC
- Weakness or faintness
- Nausea or vomiting
Bowel Prep Schedule
|Step||Scheduled Time||Actual Time Taken||Medication(s) to Take|
|1||Before 11:00 am||
|2||At 4:00 pm||
At 6:00 pm
|Plan your premedication dosing schedule and record here|