Patient education: Contrast allergy (The Basics)

What is contrast dye? — Contrast dye, or "contrast," is a liquid that makes the results of imaging tests clearer. (Imaging tests, such as X-rays, create pictures of the inside of the body). In some cases, contrast dye is put into the body before an imaging test. This can be done in different ways, including:

●By IV (into a vein)

●Through the mouth

●Through the rectum

There are different types of contrast. The type you get depends on the type of imaging test you are having.

What is contrast allergy? — Most people can get contrast with no problems. But some people are allergic to contrast. For these people, contrast can cause an allergic reaction.

Being allergic to 1 type of contrast does not mean that you are allergic to other types.

What are the symptoms of an allergic reaction to contrast? — Reactions to contrast can happen:

●Soon after getting contrast is given – These are called "immediate reactions."

●A few hours or days after getting contrast – These are called "delayed reactions."

Reactions can also be mild to severe. Severe allergic reactions are also called "anaphylaxis." When a severe reaction happens, it is usually within 20 minutes of getting contrast.

Immediate reactions happen within an hour or so of getting contrast. They can include:

●Mild symptoms:

•Itchy or swollen skin

•Hives

•Itchy or scratchy throat

•Feeling warm

•Chills

•Nausea or vomiting

•Stuffy nose

•Headache or dizziness

•Feeling anxious

●Moderate symptoms:

•Very itchy skin

•Hives or rash on a large area of skin

•Swelling in the eyes, face, or throat

•Severe nausea or vomiting

•Feeling faint

•Chest pain

•Wheezing or coughing

●Severe symptoms (anaphylaxis):

•Very low blood pressure

•Trouble breathing

•Fast or irregular heartbeat

•Swelling in the face or throat that makes it hard to breathe

•Seizures

Delayed reactions happen a few hours to a few days after getting contrast. They can include:

●Rash

●Itchy or swollen skin

Is there a test for contrast allergy? — No. There is no test that can show ahead of time if you are allergic. That's because in many cases, an allergic reaction only happens after getting a full dose of contrast. A smaller amount might not cause a reaction.

Should I see a doctor or nurse? — Most of the time, a reaction to contrast will happen while you are still at the hospital or doctor's office. The staff will know what to watch for and will be there to help you if you have problems.

But if you have signs of a delayed reaction to contrast, call your doctor or nurse for advice. Symptoms of a delayed reaction can happen up to a few days after getting contrast.

How is an allergic reaction to contrast treated? — Treatment depends on your symptoms and how severe they are. Some mild symptoms get better on their own and do not need treatment.

When treatment is needed, it might include:

●Antihistamines – These are medicines that can help with symptoms like itching or hives.

●Epinephrine – This is a medicine for treating severe allergic reactions. It is the same as the hormone adrenaline, which the body makes when you have an allergic reaction. Giving epinephrine gives the body more adrenaline than it can make on its own.

●Oxygen – If you are having trouble breathing, the staff will give you an oxygen mask to help you breathe.

Can reactions to contrast be prevented? — Certain things make you more likely to have an allergic reaction to contrast. Before you have an imaging test with contrast, talk to your doctor or nurse. Tell them about any allergies you have, including allergies to any medicines.

If you already know that you have a contrast allergy, there are ways to lower your chances of having problems again. You can:

●Write down the type of contrast that you are allergic to – If you need to have contrast again in the future, tell the staff that you have had a reaction before. This way, they can choose a different contrast, if possible.

●Take "premedications" before having another test with contrast – This means taking certain medicines before having an imaging test with contrast. In some cases, this can lower your chances of having another allergic reaction. These medicines include steroids and antihistamines. Your doctor will tell you if you can take these and give you instructions.

●Avoid imaging tests with contrast – In some cases, you might be able to have another type of test that doesn't use contrast. But this is not always possible.

●Wear or carry a medical alert ID – This is important if your past reaction to contrast was severe or life-threatening. A medical alert ID can be a bracelet, necklace, shoe tag, or card that you carry in your wallet. List your contrast allergy and any other severe drug allergies. This can help if you ever need emergency medical care and can't speak for yourself.

More on this topic

Patient education: Drug allergy (The Basics)
Patient education: Allergy skin testing (The Basics)
Patient education: Anaphylaxis (The Basics)

Patient education: Anaphylaxis symptoms and diagnosis (Beyond the Basics)
Patient education: Anaphylaxis treatment and prevention of recurrences (Beyond the Basics)