How to Get Ready for Your Virtual Colonoscopy Without Oral Contrast

Time to Read: About 9 minutes

This information will help you get ready for your virtual colonoscopy at MSK if you have an allergy to iodinated or CT contrast.

About Your Virtual Colonoscopy

A virtual colonoscopy (VC) is a test to look for signs of colorectal cancer. Your doctor will look for polyps in the lining of your colon (large intestine) and rectum (the last part of your colon). Polyps are growths that usually are not cancerous but can become cancer. Your doctor will also check parts of your abdomen (belly) and pelvis for any issues.

A VC is also sometimes called a computed tomography (CT) colonography. It uses a CT scan to take 3D pictures of the inside of your colon and rectum. This helps your doctor see inside your colon without using a scope. A scope is a flexible tube placed in the rectum during a regular colonoscopy.

Screening for colorectal cancer and polyps

Screening (checking) for colorectal cancer and polyps should start at age 45. Your doctor may recommend you screen earlier than age 45 if you have a family history of colorectal cancer. That means a close family member related to you by blood (parents, siblings, or children) has had colorectal cancer.

If your doctor finds a large polyp or growth, you may need to have a regular colonoscopy to remove it. A large polyp is 3/8 inch (1 centimeter) or bigger. Large polyps should be removed because there is a high chance they can turn into cancer.

Before Your Procedure

Pick up your prep kit

Before your procedure, you will 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.
  • 1 (8.3 ounces or 238 gram) bottle of of polyethylene glycol (MiraLAX ®).

You will also need:

  • 64 ounces of any clear liquid that isn’t red, purple, or orange. You will need to mix this with MiraLAX. Keep it at room temperature.
    • A sports drink like Gatorade® or Powerade® is a good choice. Sports drinks will help replace electrolytes that you will lose during the bowel preparation.
    • If you have diabetes, be sure to get sugar-free clear liquids.
  • A pitcher or bottle to mix the MiraLAX and 64 ounces of clear liquid.

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 usual medications. This is so you’re not taking your bowel preparation medication at the same time as your other medication. Plan to take your usual medications 1 hour before or 1 hour after taking your bowel prep medication.If you’re having trouble planning your medication time, call your healthcare provider.

Anticoagulants (blood thinners)

Blood thinners are medications that affect the way your blood clots.

Examples of common blood thinners are listed below. There are others, so be sure your care team knows all the medications you take. Do not stop taking your blood thinner without talking with a member of your care team.

  • Apixaban (Eliquis®)
  • Aspirin
  • Celecoxib (Celebrex®)
  • Cilostazol (Pletal®)
  • Clopidogrel (Plavix®)
  • Dabigatran (Pradaxa®)
  • Dalteparin (Fragmin®)
  • Dipyridamole (Persantine®)
  • Edoxaban (Savaysa®)
  • Enoxaparin (Lovenox®)
  • Fondaparinux (Arixtra®)
  • Heparin (shot under your skin)
  • Meloxicam (Mobic®)
  • Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Advil®, Motrin®) and naproxen (Aleve®)
  • Pentoxifylline (Trental®)
  • Prasugrel (Effient®)
  • Rivaroxaban (Xarelto®)
  • Sulfasalazine (Azulfidine®, Sulfazine®)
  • Ticagrelor (Brilinta®)
  • Tinzaparin (Innohep®)
  • Warfarin (Jantoven®, Coumadin®)

Contrast dye

Contrast is a special dye that makes it easier for your doctor to see differences in the organs inside your body. Oral contrast dye is sometimes given during bowel preparation for a VC. Since you’ve had a reaction to iodinated or CT contrast dye in the past, you will not use oral contrast dye during your preparation.

If you’re having a VC with oral contrast, read the resource How to Get Ready for Your Virtual Colonoscopy .

For people who take premedication

You may still get intravenous (IV) contrast dye for your VC. Call your healthcare provider 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 healthcare provider if you have any questions.

Diabetes medication

  • If you take insulin or other medications for diabetes, you may need to change the dose. Ask the healthcare provider who prescribes your diabetes medication what to do the day before and morning of your procedure. Tell them you will be following a clear liquid diet the day before your procedure.
  • If you monitor your blood sugar (glucose) level, ask your healthcare provider if you should stay on the same monitoring schedule. Call them if your blood sugar falls below 70.

Take devices off your skin

You may wear certain devices on your skin. Before your scan or procedure, device makers recommend you take off your:

  • Continuous glucose monitor (CGM)
  • Insulin pump

Talk with your healthcare provider about scheduling your appointment closer to the date you need to change your device. Make sure you have an extra device with you to put on after your scan or procedure.

You may not be sure how to manage your glucose while your device is off. If so, before your appointment, talk with the healthcare provider who manages your diabetes care.

3 Days Before Your Procedure

Avoid certain foods

Do not eat foods that are hard to digest. They may make it hard for your healthcare provider to see your organs in the pictures taken during your VC. You may need to have the procedure again if this happens.

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.
  • Popcorn.
  • Potato skins.
  • Whole grains (such as oatmeal, brown rice, quinoa, or wheat bread).
  • Seeds (such as poppy or sesame).
  • Nuts.

The Day Before Your Procedure

Prepare Your MiraLAX Bowel Preparation

On the morning of the day before your procedure, mix all 238 grams of the MiraLAX powder with 64 ounces of a room temperature clear liquid. Mix it until the MiraLAX powder dissolves.

Once the MiraLAX is dissolved, you can put the mixture in the refrigerator. Many people find it tastes better when it’s chilled.

Do not mix the MiraLAX earlier than the morning of the day before your procedure.

Start your bowel preparation

During your bowel preparation, you will take laxatives and contrast medication. 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 hard to see polyps or other problems inside your colon. If this happens, you may need to do the procedure again.

If you have any questions, call your healthcare provider’s office.

Follow a clear liquid diet

You will need to follow a clear liquid diet the day before your procedure. A clear liquid diet includes only liquids you can see through. You can find examples in the “Clear Liquid Diet” table.

While you’re following a clear liquid diet:

  • Do not eat any solid foods.
  • Try to drink at least 1 (8-ounce) cup of clear liquid every hour you’re awake.
  • Drink different types of clear liquids. Do not just drink water, coffee, and tea.
  • Do not drink anything red, purple, or orange.

You can drink as many clear liquids as you like between each step of your bowel preparation. Stop drinking clear liquids at midnight.

Clear Liquid Diet
  OK to Drink Do Not Drink
  • Clear broth, bouillon, or consommé.
  • Clear packaged vegetable, chicken, or beef broth-mix.
  • Any products with pieces of dried food or seasoning.
  • Gelatin, such as Jell-O®.
  • Flavored ices.
  • Sweeteners, such as sugar or honey.
  • Anything red, orange, or purple.
  • Water.
  • Clear fruit juices, such as white cranberry, white grape, apple.
  • Soda, such as ginger ale, 7-Up®, Sprite®, and seltzer.
  • Sports drinks, such as Gatorade®, and Powerade®.
  • Black coffee.
  • Tea.
  • Clear liquid protein drinks.
  • Juice with pulp.
  • Nectars.
  • Smoothies or shakes.
  • Milk or cream.
  • Alcoholic beverages.
  • Anything red, orange, or purple.

Follow your bowel prep medication schedule

Start taking your bowel preparation medication the day before your VC. Follow the medication schedule in this section.

You may need to change the time you take your usual medications. If you usually take your medications at the time you’re supposed to take one of your bowel preparation medications, plan to take your usual medications 1 hour before or 1 hour after. If you’re having trouble planning your medication time, call your healthcare provider.

If your healthcare provider 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 healthcare provider.

If you have any questions, call 212-639-7280. If the office is closed, call 212-639-2000 and ask for the Radiology Body fellow on call.

Bowel prep schedule

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 , take 2 (5 milligram) bisacodyl tablets.

  • Take them with 1 (8-ounce) glass of clear liquids.
  • Do not chew or crush them.
  • Do not take them within 1 hour of taking an antacid (medication to relieve heartburn or stomach pain). Examples of antacids include calcium carbonates (such as Tums®) and histamine-2 blockers (such as Zantac®). Ask your healthcare provider for more information.

The bisacodyl tablets will make you have a bowel movement (poop) about 6 to 8 hours after you take them. This will help the laxative you take in Step 2 and Step 3 work better. You can take these tablets and still do normal activities. They will rarely cause diarrhea (loose or watery bowel movements).

Step 2: First half of the MiraLAX mixture

At , drink half of the MiraLAX mixture.

  • You may want to drink it with a straw to lessen the taste.
  • This is a laxative, so you should start having bowel movements more often. Your stool (poop) 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 do not start having bowel movements within 2 hours after completing Step 2, call your healthcare provider.
  • 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: Other half of the MiraLAX mixture

At , drink the other half of the MiraLAX mixture. Drink it the same way you drank the first half.

Drink at least 4 to 6 cups (32 to 48 ounces) of clear liquids over the next 2 hours.

Now your stool (poop) 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.

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

Many staff members will ask you to say and spell your name and birth date. This is for your safety. People with the same or a similar name may be having surgery on the same day.

When it’s time to change for your procedure, you will get a hospital gown to wear.

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 see inside it. Your technologist will ask you to change positions a few times. This is to help move the air or gas throughout your colon. You will lie on your side, back, and abdomen (belly).

The VC is not 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.

Your technologist will ask you to hold your breath for about 10 seconds while the CT scanner takes pictures. They will take pictures of your abdomen and pelvis in at least 2 different positions. This is usually while you’re on your back and stomach.

After Your Procedure

  • You may go back to your normal diet after your procedure.
  • You may feel some cramping in your stomach. 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 (Monday through Friday) to get your results. The doctor who sent you for your VC will call you when your results are ready.

When to Call Your Healthcare Provider

Call your healthcare if you have:

  • A fever of 101° F (38.4° C) or higher.
  • Stomach pain, other than mild cramping.
  • Bleeding from your rectum, A small amount of blood on toilet paper is normal 24 hours after your VC.
  • Weakness or faintness.
  • Nausea (feeling like you’re going to throw up).
  • Vomiting (throwing up).

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Last Updated

Monday, February 13, 2023