Preparation guidelines for a CT scan depend on the type of scan you’re having. If you’re having a bowel scan or a scan with contrast dye, you may need to adjust your diet.

Preparation for a CT scan (aka CAT scan) will depend on the type of scan you’re having and the part of the body involved. A doctor may schedule a CT scan for a few days out or in some cases, the scan may occur on the same day as your initial visit.

CT scans don’t usually require much prep. What’s important is that the radiology team can get clear images and that you’re safe during the procedure. Depending on which area of your body the scan will focus on, this may involve more advanced prep, like fasting or clearing your bowels.

Do not forget to tell your doctor…

As soon as a doctor lets you know they want to schedule you for a CT scan, be sure to let them know if any of the following apply to you:

  • You’re pregnant or might be.
  • You’re breastfeeding or chestfeeding.
  • You have asthma.
  • You have diabetes.
  • You have kidney or thyroid problems.
  • You’re currently taking any medications.
  • You’ve previously had an allergic reaction to any contrast dyes.

You’ll need to adjust your diet if you’re having a CT scan of your bowels, such as CT enterography or CT colonography, or if you’re having a CT scan with contrast.

Bowel CT scan

A CT scan of your bowels may require several days of bowel preparation. This may include:

  • switching to a clear liquid diet a few days before the procedure
  • fasting the night before and the morning of the scan
  • taking a laxative, enema, or suppository to clear your bowels

However, a 2023 study found that CT colonography can be effective without diet restrictions. Researchers provided a laxative the night before and used a process called fecal tagging to help them distinguish stool from other items of concern on the scan.

CT scan with contrast

Some CT scans use a contrast dye to enhance specific areas or structures.

Your doctor may advise you not to eat or drink anything for several hours before your test. Some imaging facilities may allow you to drink water if needed.

Some medical professionals previously thought that eating or drinking before a CT scan with contrast increased the risk of nausea, vomiting, and aspiration pneumonia. However, recent research suggests this is not the case, so some places no longer follow this requirement.

Talk with a doctor about what medications you take. Depending on the type of CT scan you’re having, you may need to adjust your dosing schedule or stop taking some a few days before your scan.

This includes over-the-counter medications. For example, you may need to stop taking metformin and nonsteroidal anti-inflammatory drugs (NSAIDs), like aspirin or ibuprofen, as these can increase the risk of kidney damage when taken with the dye.

People with diabetes may also have to adjust their insulin schedule.

You’ll want to wear loose, comfortable clothing. You cannot have anything with metal in it, including:

  • jewelry
  • zippers
  • bras with metal wires
  • hair clips
  • belt buckles
  • buttons or other fasteners
  • hearing aids
  • dentures

If you have any of these items on you, you’ll need to remove them before the scan.

Braces and fillings are OK for a CT scan, but you should not wear a retainer.

Doctors use coronary CT angiography, also called a coronary CTA, to view the blood vessels in your heart.

In preparation for this type of CT scan, you’ll need to avoid anything that increases your heart rate or affects coronary blood flow, as this can make it more challenging to get accurate images. You’ll also need to avoid anything that increases the risk of kidney damage.

Typical recommendations include:

Your medical team may give you a beta-blocker to take 2 hours before your scan to help reduce your heart rate.

A CT scan usually takes 10 to 30 minutes, and you should get results within a few days. If results come back quickly or if they take a while, try not to assume the worst. It’s best to wait for your doctor to explain the results and next steps.