Symptoms of Contrast Dye Allergy and What to Do

A contrast dye allergic reaction can occur after a diagnostic imaging test, such as magnetic resonance imaging (MRI) or computed tomography (CT) scan. The contrast dye used with these tests is an iodine-based or gadolinium-based substance that's given through a vein to help internal organs and 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, though delayed reactions are possible. Symptoms can be serious, such as skin reactions or trouble breathing.

Symptoms

Contrast dye can cause the body to release chemicals such as histamine. This triggers allergic-like symptoms that are not common but have been observed with contrast use.

Mild reactions to contrast dye occur in 3% to 15% of people receiving contrast. Most of these reactions include:

• A feeling of warmth or flushing through the body
• Nausea
• Vomiting
• Itchiness
• Metallic taste in your mouth
• A sense that you're urinating but you aren't

There may be some discomfort when the IV line is inserted, but you shouldn’t feel pain when the dye is injected.

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, but they can be life-threatening.

Symptoms of a moderate or severe reaction (referred to as anaphylaxis) that can require urgent medical care include:

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

Risk Factors

Certain factors appear to put some people at higher risk for contrast dye allergy or complications. It is more likely to affect the kidneys with contrast-induced nephropathy (CIN) in people diagnosed with:

• Heart disease
• Chronic kidney disease
• Diabetes

Older people are more likely to experience CIN and adverse reactions. So are those who take beta blocker medications. There also may be a higher risk for people with asthma and underlying allergies, and those who have had past reactions to contrast dye.

Treatment

The treatment for contrast dye allergy is based on symptoms, meaning that treatment is given to alleviate the specific effects of the reaction.

Treatment may include the following:

• Injectable epinephrine or epinephrine nasal spray (Neffy) 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.

Contrast dye allergies are unpredictable and small test doses do not indicate whether or not a reaction will occur, even in people who may have had similar procedures in the past. There are steps you can take, however, if you've had contrast dye reaction before.

Your healthcare provider may recommend using a different type of contrast or taking medications before the procedure. These drugs can include:

• Oral corticosteroids such as prednisone
• Antihistamines such as Benadryl (diphenhydramine) or Zyrtec (cetirizine)
  

Keep in mind that a contrast dye allergy can only be diagnosed after symptoms have occurred. Otherwise, it's only possible to determine that a person is at increased risk of a reaction. Skin tests may help to identify a problem in some cases.

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.