Iodine Allergy Myth

Adverse reactions to iodinated contrast do.  These are entirely unrelated to shellfish allergy (a reaction to tropomyosin, a muscle protein in the shellfish, not to the iodine in them).  This is a longstanding myth in the medical community and difficult to dispel.  To some degree, asthma will increase the possibility of a contrast reaction.  Sensitivity to Betadine® and other iodine-containing solutions is unrelated to reactions to iodinated radiographic contrast agents.

From the American Academy of Allergy Asthma and Immunology. Once a person has one contrast reaction they are at very high risk for more unless treated. The reactions do tend to be worse in people who are dehydrated (dried out) when they are given the contrast in their veins. These reactions are not caused by iodine and are not more common in people with shellfish or any other true allergy. They can be minimized by pretreatment with antihistamines and oral steroids and/or using non-ionic contrast material that, interestingly, still has iodine in it.

For more information, a very nice discussion is found here.  Or search for "iodine" in the Ask the Expert page of the website of the American Academy of Allergy Asthma and Immunology.

Most contrast reactions are non-allergic and consist of flushing, hives, itching.  These are considered minor reactions.

If a patient needs a contrast-enhanced exam and has a history of a previous major contrast reaction, premedication with Prednisone beginning the day prior to the exam can be given.  Additional considerations include how long ago the previous reaction occurred.  Years ago, the only contrast agents in use were ionic iodinated contrasts.  Currently we use nonionic agents, with a significant reduction in adverse reactions.  As for MRI contrast agents, these are gadolinium-based and are unrelated to previous reactions with iodinated contrast agents.