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ACAAI > Patients & Public > Resources > Ask the Allergist

Is Shellfish Allergy Related to Iodine?

Q. I am a 44-year-old man with a known shellfish allergy for more than 20 years.

I have always been told that due to my severe reaction to shellfish I was also allergic to iodine. Now, I need to have a procedure that requires injecting me with an intravenous iodine-based contrast, and I told my doctor that I am hesitant to have this procedure due to my shellfish allergy. My doctor has tried to assure me that my shellfish allergy has nothing to do with me being allergic to iodine. What is your opinion?

A. Years ago doctors believed that shellfish allergy stemmed from increased amounts of iodine present in the shellfish, so patients with a shellfish allergy were told to avoid iodine. But we now know that having a reaction to an iodine-based contrast dye is not at all the same as an allergy to shellfish.

If you are allergic to shellfish, specific proteins found in these foods are the allergens, not iodine. There is about a three percent chance that if you are allergic to shellfish you will have a reaction to contrast dyes, but this percentage is about the same in people with no known shellfish allergy. In other words, allergic people can react to multiple different things! If your doctor believes you need this procedure to make a definitive diagnosis, you should undergo the procedure. Ask your doctor to speak to the radiologist prior to scheduling the procedure and explain your fears. The radiologist may recommend pre- medicating you prior to the procedure, in an effort to alleviate your anxiety and any possibility of an allergic reaction.

For your shellfish allergy, you should always carry a prescription epinephrine self-injector, and be comfortable with using this in the event of a reaction.