My patient with abdominal pain needs a CT scan with IV iodinated contrast, but reports a “shellfish” allergy? Is she at high risk of allergic reaction to IV contrast?

Patients with shellfish allergy appear not to have a significantly higher rate of allergic reactions to iodinated contrast media compared to patients with history of atopy, such as asthma or other food allergies 1,2.  When true shellfish allergy occurs, it is caused by an immunological reaction to the protein, not iodine, content of the food ingested.  “Iodine allergy” cannot exist because iodine is found throughout our bodies and is essential to life. 

The typical IV contrast-related adverse reaction is caused by non-IgE-mediated mast cell and basophil degranulation due to the high osmolality of these agents. Because the resultant “anaphylactoid” reaction is not associated with prior immune system memory, its risk is not increased by previous exposure to IV contrast.  Premedication with corticosteroids and diphenhydramine may be effective in reducing the risk of such reactions, but is not routinely recommended in patients with isolated history of shellfish allergy2.

 

References

  1. Schabelman E, Witting M. The relationship of radioconstrast, iodine, and seafood allergies: a medical myth exposed. J Emerg Med 2010;39: 701-707.
  2. Westermann-Clark E, Pepper AN, Talreja N, Lockey RF. Debunking myths about “allergy” to radioconstrast media in an academic institution. Postgrad Med 2015;127:295-300.
My patient with abdominal pain needs a CT scan with IV iodinated contrast, but reports a “shellfish” allergy? Is she at high risk of allergic reaction to IV contrast?

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