Computed Tomography (CT) Scan

This information will help you prepare for your computed tomography (CT) scan with or without oral or intravenous (IV) contrast.

CT scans take a fast series of x-ray pictures. The x-ray pictures are combined to create pictures of the soft tissues and bones in the area that was scanned. Depending on the reason for your CT scan and which part of your body your doctor needs to see, he or she may suggest you have the CT with contrast. Contrast is a special dye used to make it easier for your doctor to see differences in your internal organs. There are types of contrast that you drink, called oral contrast, and types you can receive in your IV, called IV contrast.

Oral Contrast

  • Before Your CT Scan

If your doctor has ordered a CT with oral contrast, you’ll be asked if you are allergic to iodine or artificial sweeteners (either Fontana® or Splenda®) when you check in for your appointment. Depending on whether you have these allergies, we will give you one of the oral contrast solutions listed below. Both work the same way, are used for the same purpose, and are safe even if you have diabetes.

  • Iodine mixed with Crystal Light®, which contains aspartame.
  • Diluted barium sweetened with saccharin. Diluted barium does not have iodine.

You will start drinking the oral contrast 45 to 60 minutes before your CT scan. This will allow time for the solution to move into your bowels (intestines).

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IV Contrast

  • Before Your CT Scan

If your doctor ordered a CT scan with IV contrast, the contrast material will be injected into a vein. In most cases it will be injected through an IV catheter (thin, flexible tube), on the inside of your elbow or lower part of your arm, but there are certain types of implanted ports and catheters which may also be used. IV contrast can be given to most people without any problems, but there are some risks. Most reactions are similar to an allergic reaction, so be sure to tell your doctor or nurse about any allergies you have or if you’ve had a reaction to IV contrast in the past.  If your doctor feels that he or she needs to give you medication(s) to reduce your risk of having a reaction, instructions will be given to you in a resource called Preventing an Allergic Reaction to Contrast Media.

If you are breastfeeding, you may choose to continue after your CT scan with IV contrast. If you have questions or would like to discuss contrast and breastfeeding, talk with your radiologist on the day of your CT scan.

To determine whether you need a blood test before your CT scan, a member of your healthcare team will ask you if you:

  • Have kidney disease
  • Have poor kidney function
  • Have had surgery on your kidneys
  • Have diabetes
  • If you are taking a medication to control your diabetes called metformin

If you answer yes to any of these questions, or if you are 70 years or older, you will need to have a blood test called a serum creatinine before your CT scan. If the doctor who ordered your CT scan did not check your serum creatinine ahead of time, we will check it before you have your CT scan. For your safety, your CT scan will not be done until we have those results.

Common reactions to IV contrast

Common reactions to IV contrast are mild. You might experience:

  • A feeling of warmth during the injection.
  • A metallic taste in your mouth.
  • A mild allergic reaction, such as hives. This usually goes away by itself, but it may be treated with medication such as diphenhydramine (Benadryl®).
  • Some leaking of the contrast outside of your vein. Depending on how much contrast leaks, the side effects can be minor or moderate. Leaking contrast can result in swelling or a mild skin reaction, similar to welts. Treating these effects quickly can lessen their severity. If you have burning or pain while you’re getting the injection or after it’s finished, tell your doctor or nurse. He or she will apply a thermal compress and ask you to keep your affected arm elevated. This will help your body absorb the contrast and lessen any harm.

Uncommon reactions to IV contrast

  • Trouble breathing. This happens in about 1 in 5,000 people. You could be short of breath, or have swelling in your face. These reactions are treated immediately by your healthcare providers.
  • Change in your kidney function. If you have kidney disease or poor kidney function, tell your doctor or nurse as soon as possible, such as when you schedule your test.

Rare reactions to IV contrast

Severe reactions to contrast media are extremely rare.

  • A severe allergic reaction may cause death. This can occur in about 1 in 100,000 people. There is no test that can be done to predict it. There is no way to know who may have a severe allergic reaction.

After your CT scan

If you’re going home after your CT scan, your temporary IV catheter will be removed and a dressing will be applied. You can remove the dressing after an hour as long as there is no bleeding.

If you’re not feeling well, or if you have any questions or concerns, talk with your nurse or technologist. You can stay in Radiology and be monitored until you feel better. Drink plenty of liquids, especially water, for 24 hours after your CT scan. Drinking water will help flush your kidneys.

If you take a drug containing metformin, you will be given information regarding when you can start taking it again.  Most people will have to stop taking the medication for 48 hours, but some people will require a blood test first.

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