A recent EMedHome Clinical Pearl sheds some light on the alleged relationship between “allergies” to radiocontrast/iodine and seafood allergies.
The pearl noted that iodine is found throughout our bodies and is added to most kinds of table salt used in the United States. Our thyroid glands need iodine to function properly. While seafood contains iodine, the allergies to seafood are due to muscle proteins, not to the iodine.
Because reactions to IV contrast are not IgE-mediated, they are not considered “anaphylactic” or “allergic.” Sensitization does not occur since the reactions are not immune-mediated. In other words, your immune system won’t “remember” a prior reaction to contrast material.
Administration of steroids has no effect on whether a severe reaction will occur. Since the reaction is not “allergic”, Benadryl probably won’t have any effect, either – although this was not specifically stated in the study.
Severe reactions to contrast media occur in 0.02-0.5% of cases and deaths occur in 0.0006-0.006% of patients (something else to consider when deciding whether to undergo repeated CT scans), but serious reactions and death are not related to allergies to iodine/seafood or to prior reactions to contrast media.
One recently-published study used to create the pearl dispels this “medical myth” quite nicely.