This resource will help you get ready for your virtual colonoscopy without oral contrast at MSK. You’ll have a VC without oral contrast if you have an allergy to iodinated or CT contrast. A VC is also sometimes called a computed tomography (CT) colonography.
About your virtual colonoscopy
A virtual colonoscopy is a test to look for signs of colorectal cancer. A VC uses a CT scan to take 3D pictures of the inside of your colon (large intestine) and rectum. Your rectum is the last part of your large intestine. The images from the scan help your doctor see inside your colon without using a scope. A scope is a flexible tube placed in the rectum during a regular colonoscopy.
During a VC, your doctor will look for polyps (growths) in the lining of your colon and rectum. Polyps are not often cancerous, but they can become cancer. Your doctor will also check parts of your abdomen (belly) and pelvis for any issues.
Screening for colorectal cancer and polyps
You should start screening (getting checked) for colorectal cancer and polyps 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 blood relative has had colorectal cancer. A blood relative is a close family member related to you by blood, such as a parent, sibling, or child.
If your doctor finds a large polyp or growth, you may need a regular colonoscopy to remove it. A large polyp is 3/8 inch (1 centimeter) or bigger. It’s important to have large polyps removed because there is a high chance they can turn into cancer.
What to do before your procedure
Pick up your prep kit
Before your VC, you will need to clean out (empty) your colon using a prep kit. 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:
- 1 (64 ounce) bottle of any clear liquid that is not red, purple, or orange. 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 (prep). If you have diabetes, be sure to get sugar-free clear liquids. Keep it at room temperature.
- A pitcher or bottle that can hold 64 ounces of liquid.
You may also need to pick up premedication for your VC prep. Your doctor may tell you that you’ll need to take contrast dye premedication for your VC. If they do, pick up your premedication at the pharmacy when you pick up the prep kit.
Ask about your medicine
You may need to change the time you take your usual medicines. This is so you’re not taking your bowel prep medicine at the same time as your other medicine. Plan to take your usual medicines 1 hour before or 1 hour after taking your bowel prep medicine. If you’re having trouble planning time to take your medicine, call your healthcare provider.
Anticoagulants (blood thinners)
Blood thinners are medicines that affect the way your blood clots.
Here are some examples of blood thinners. There are others, so be sure your care team knows all the medicines you take. Do not stop taking your blood thinner without talking with a member of your care team.
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Contrast dye
Contrast is a special dye that makes it easier for your doctor to see differences in your organs. Some people get oral contrast dye during bowel prep for a VC. Since you’ve had a reaction to iodinated or CT contrast dye, you will not get oral contrast dye.
If you’re having a VC with oral contrast, read How to Get Ready for Your Virtual Colonoscopy (VC).
For people who take premedication
You may still get intravenous (IV) contrast dye for your VC. Talk with your healthcare provider about whether you’ll get IV contrast.
If you’re getting IV contrast and you usually take premedication, you’ll need to take premedication before your VC. Call your healthcare provider if you have any questions.
Diabetes medicine
If you take insulin or other medicine for diabetes, you may need to change the dose. Ask your diabetes healthcare provider what to do the day before and morning of your procedure. Tell them you’ll be following a clear liquid diet the day before your procedure. If you monitor your blood glucose (blood sugar), ask them if you should stay on the same schedule. Call them if your blood glucose falls below 70 mg/dL (milligrams per deciliter).
Take devices off your skin
You may wear certain devices on your skin. Before your procedure, surgery, or scan, some 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 to bring an extra device with you to put on after your procedure, surgery, or scan.
You may not be sure how to manage your glucose (blood sugar) while your device is off. If so, before your appointment, talk with the healthcare provider who manages your diabetes care.
What to do 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.
What to do the day before your procedure
Prepare your MiraLAX bowel prep
Mix all 238 grams of the MiraLAX powder with 64 ounces of a room temperature clear liquid. Do this in the morning the day before your procedure. 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 prep
During your bowel prep, 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 prep. Stop drinking clear liquids at midnight.
| Clear Liquid Diet | ||
|---|---|---|
| OK to Drink | Do Not Drink | |
| Soups |
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| Sweets |
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| Drinks |
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Follow your bowel prep medicine schedule
Start taking your bowel prep medicine the day before your VC. Follow the medicine schedule in this section.
You may need to change the time you take your usual medicines. If you usually take your medicine at the time you’re supposed to take one of your bowel prep medicines, plan to take your usual medicine1 hour before or 1 hour after. If you’re having trouble planning time to take your medicine, call your healthcare provider.
If your healthcare provider told you to take contrast dye premedication, you’ll need to plan when to take it. Talk with your healthcare provider if you need help planning this.
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.
Before 9 a.m.
Take 2 (5 milligram) bisacodyl tablets with 1 (8-ounce) glass of clear liquids. Do not chew or crush them.
Do not take the tablets within 1 hour of taking an antacid. Antacids are medications to relieve heartburn or stomach pain). Examples of antacids include:
- Calcium carbonates, such as Tums®.
- Histamine-2 blockers, such as Zantac®.
Talk with your healthcare provider to learn more.
The bisacodyl tablets will make you have a bowel movement (poop) about 6 to 8 hours after you take them. This will help the laxatives you take later work better. The tablets will rarely cause diarrhea (loose or watery bowel movements). You can still do normal activities after taking these tablets.
At 1 p.m.
Drink the first 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. You should start having bowel movements within 2 hours after you finish the first half of the mixture. If you don’t, call your healthcare provider.
Put petroleum jelly (Vaseline®) or A & D® ointment on 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.
At 4 p.m.
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.
After drinking it, your stool (poop) should be more liquid and yellowish-clear. This is a sign that your bowels are getting cleared. If your bowels are not getting cleared, call 212-639-7280 and ask to talk with a nurse or the fellow on call.
After midnight (12 a.m.)
Do not eat or drink anything after midnight except for your medicine. If you take medicine, take it with a small sip of water.
What to do the day of your procedure
Do not eat or drink anything. If you take medicine, take it as you normally would with a small sip of water.
What to expect when you arrive
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. A staff member will take you into the CT exam room and help you lie on the CT exam table.
In the exam room
A nurse or doctor will gently place a small tube into your rectum. It will feel like you’re having a rectal exam. They’ll secure the tube to your leg or buttocks. 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 during the procedure. This is to help move the air or gas throughout your colon. You will lie on your side, back, and abdomen (belly).
Your technologist will ask you to hold your breath for about 10 seconds while the CT scanner takes pictures. They’ll take pictures of your abdomen and pelvis in at least 2 different positions. This is usually while you’re on your back and stomach.
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.
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.
You may go back to your normal diet after your procedure.
Getting your results
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).