It is not unusual to have significant adverse reactions to contrast media utilized in imaging. These reactions appear to be massive anaphylactic reactions that can even be fatal. Initially it was felt that these were reactions to the Iodine in the contract media, and that these were allergic in nature. Then the misconception that this allergy to Iodine would cross react with sea food allergies, as seafood is high in Iodine content. Iodine is a trace mineral that is in highest concentration in the ocean.
In reality, Iodine is an element that has no potential to even be a true allergen. The real reaction to contrast media is a mast cell and basophil degranulation of histamine due to the hypertonicity of the contrast media. The reaction clinically mimics an anaphylactic reaction, but is in reality just a histamine spill due to the IV administration of a hyperosmolar solution. It is an “anaphylactic like” or anaphylactoid reaction. And any correlation with Sea Food or shellfish is completely false. True shellfish or crustacean allergy is really an allergy to a muscle protein (troponin).
Patients who are atopic and asthmatic, of course, have a higher risk of reacting. There are prophylactic steps, such as steroids and antihistamines, that can lessen the risk.