Contrast Dye Allergy: Symptoms and What to Do

A contrast dye reaction can occur after a diagnostic imaging test, such as an MRI or CT scan. Contrast dye is an iodine-based or gadolinium-based substance that's given through a vein to help internal structures stand out during scans. Studies show that less than 1% of people who receive contrast dye will have a serious allergic reaction.

Most reactions occur within an hour of receiving contrast dye and many occur within the first five minutes. However, there can sometimes be delayed reactions that occur up to a week later. Symptoms can include serious allergic-like symptoms, such as skin reactions or trouble breathing.

This article will further explore the symptoms of a contrast dye allergic reaction, risk factors for reactions, and how a contrast dye allergy is treated.

Symptoms of Contrast Dye Allergy

Contrast dye acts to directly release chemicals, such as histamine. This triggers allergic-like symptoms. A true allergy occurs due to the production of antibodies, which are specialized immune proteins. This typically does not happen with contrast dye reactions, but it has been described.

The severity of a contrast dye reaction can range from mild to severe and life-threatening. Mild reactions are relatively common, occurring in 3% to 15% of people receiving contrast. Most of these reactions include:

• A feeling of warmth
• Nausea
• Vomiting

Generally, symptoms of a mild reaction occur for a short period and don't require treatment. Severe reactions occur in less than 1% of people receiving contrast. Symptoms of a moderate or severe reaction that require urgent medical care include:

• Severe vomiting
• Hives
• Difficulty breathing
• Swelling in the throat
• High-pitched sound when breathing
• Convulsions
• Fast heart rate
• Loss of consciousness

Some of these symptoms may occur if the allergic reaction causes cardiac arrest.

Risk Factors

These factors appear to put people at higher risk for adverse or allergic reactions to contrast dye:

• Past reactions to a similar type of contrast
• Having asthma
• Having allergies
• Having heart disease
• Having kidney disease
• Taking beta-blockers, which are medications commonly used for a variety of conditions, including heart conditions

Older adults also have an increased risk for severe reactions.

Treatment

The treatment is symptomatic, meaning that treatment is given to alleviate the specific effects of the reaction.

Treatment may include the following:

• Injectable epinephrine, which relaxes tubes of the lungs called bronchi, allowing easier breathing
• Antihistamines, drugs that block the actions of histamine
• IV fluids for treatment of low blood pressure and shock

Prevention

Unfortunately, there is no test available to diagnose a contrast dye allergy in advance. Skin testing and blood testing to look for allergies are often not helpful in the diagnosis.

Reactions are unpredictable and small test doses do not indicate whether or not a reaction will occur when a regular amount is given. There are even reports of severe, life-threatening reactions to contrast dye occurring after a person had tolerated a small test dose of IV dye.

There are steps you can take, however, if you've had a non-severe reaction to contrast dye in the past and need to use a similar type for more imaging. In this instance, your medical provider will likely recommend pre-medication. This involves taking medication in advance of receiving contrast dye to lower the risk of a reaction.

It is common to be treated with a pre-medication combination of oral corticosteroids, such as prednisone, and antihistamines, such as Benadryl (diphenhydramine).

If you've had a history of severe reactions, your healthcare provider will avoid using the same class of contrast dye except in specific circumstances. Typically, the reaction is agent-specific and you might be able to use another iodinated contrast from a different class that is low in osmolarity and ionicity if needed.

Summary

IV contrast dye is a solution that's put into the bloodstream during medical imaging in order to make internal structures, such as organs and blood vessels, easier to see.

Mild reactions to contrast dye are fairly common and don't require treatment. In rare cases, severe and life-threatening emergencies can occur.

If you're concerned about a potential reaction to contrast dye, talk to your healthcare provider about the risks and benefits of having a test with contrast and whether alternatives are available. If you have a history of reactions to contrast dye, always make your healthcare provider aware of any previous reactions.