Myth: Radiocontrast media reactions are related to shellfish allergy.
Busted! Patients with a history of allergy to shellfish are not at increased risk for anaphylaxis from iodinated contrast media. This myth stems from the false assumption that an iodine allergy is the common cause of contrast media and shellfish allergy. In fact, iodine is not an allergen and is structurally unrelated to the tropomyosin proteins which can cause anaphylactic reactions to shellfish. Although it is clear that contrast media can cause a variety of reactions, the mechanism of most of these is poorly understood and is not due to ‘iodine allergy’. Individuals with any allergic condition are at higher risk of contrast media reactions, regardless of a history of allergy to seafood. Fortunately, reactions to contrast media are quite low.
In some patients scheduled for procedures using contrast dye, precautions should be taken, such as premedication with antihistamines or steroids or using low osmolal contrast material (LOCM) agents. So who deserves these precautions? Empiric use of LOCM agents for all intravascular procedures has become widespread and has largely eliminated the need for premedication. In settings where LOCM agents are not routine, nonionic LOCMs or iso-osmolal agents should be considered for patients with asthma and patients taking beta-blockers, interleukin-2, or NSAIDS (eg. Aspirin, ibuprofen). In addition, nonionic LOCM agents should be considered in patients with a previous history of serious reactions to radiocontrast media, patients receiving contrast by power injector, or any other circumstance in which the clinician believes that it is indicated. In the absence of a history of immediate hypersensitivity reactions to contrast media in the past, empiric premedication with antihistamines and steroids is generally not indicated.
American College of Radiology Committee on Drugs and Contrast Media. ACR Manual on Contrast Media, 5th ed, American College of Radiology, Reston VA 2004. p.5.
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Lang DM, Alpern MB, Visintainer PF, Smith ST. Elevated risk for anaphylactoid reaction from radiographic contrast media associated with both beta blocker exposure and cardiovascular disorders. Arch Intern Med. 1993;153:2033-40.