This information explains what to expect if you receive intravenous contrast media for a computed tomography (CT) scan or other imaging study.
Your doctor would like you to have a CT scan or other imaging study. You will receive contrast media that has iodine. It will be injected into your bloodstream through a plastic catheter placed into a vein. The catheter is usually put on the inside of your elbow or on the back of your hand. The contrast media helps your doctor interpret the CT scan or other imaging study.
Benefits of Contrast Media
Contrast media can make a diseased area stand out from surrounding tissue. It makes it easier to see abnormal tissue. This may allow your doctor to make a more accurate diagnosis, treatment plan, or both.
Risks of Contrast Media
Contrast media can be given to most patients without any problems, but there are some risks. These risks range from mild to severe. The frequency of patient reactions varies from common to extremely rare. Most reactions are a kind of allergy. Tell your doctor or nurse about any allergies you have. Also, tell your doctor or nurse if you have had a reaction to contrast media in the past.
Common, but mild reactions
- A warm feeling throughout your body
- 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 diphenhydramine (Benadryl®) or a similar medication.
- Leakage of the contrast media outside the vein. Depending on how much fluid leaks, the side effects can be minor or moderate. Minor side effects include swelling or a mild skin reaction similar to welts. Prompt treatment can lessen the severity of these effects. If you have burning or pain, tell your doctor or nurse. Apply a cold compress and raise the affected arm. This helps your body reabsorb the contrast and lessens any harm.
Moderate, but uncommon reactions
- Trouble breathing. This happens in about 1 in 5,000 patients. You could be short of breath or have facial swelling. These reactions are treated immediately.
- Changed kidney function. Tell your doctor or nurse if you have kidney disease or poor kidney function.
Severe, but extremely rare reactions
- A severe allergic reaction that may cause death. This can occur in about 1 in 100,000 patients. It is extremely rare. There is no test that can be done to predict it. There is no way to know who may have this side effect.
If You Are or May Be Allergic to Contrast Media
Your doctor may give you medication to reduce the risk of a reaction. We call these “premeds.” He or she may also decide not to use contrast. Alternatives are described below. If you will get premeds, you will be given a prescription for one of the following:
You will take a total of 3 pills before your appointment. Take the first pill 13 hours before your appointment, take the second pill 7 hours before your appointment, and take the third pill 1 hour before your appointment.
You will also need to take 50 mg of diphenhydramine (Benadryl®) 1 hour before your appointment. Make sure someone takes you home afterwards. The diphenhydramine (Benadryl®) may make you feel sleepy.
You will take a total of 2 pills. Take the first pill 12 hours before your appointment and take the second pill 2 hours before your appointment.
If you've been instructed to take either of the medications above, increase the amount of fluid you drink the night before your procedure.
Alternatives to Contrast Media
Imaging can be done without contrast media. In this case, an abnormal area may not stand out as clearly from the surrounding tissue. Therefore, the diagnosis or treatment plan may not be as accurate. A different test can be done, but it may not be as precise. Your nurse or doctor will review this information with you. Be sure to ask any questions that you have about contrast media.