New Research Shatters Age-Old Iodine Allergy Myth

A new study led by pharmacists from FDB (First Databank) found that avoiding contrast dyes for imaging tests isn’t necessary if clinicians are concerned about iodine allergies in patients. The study further refutes the concept of iodine allergies, citing no verified documented cases of allergic reactions to iodine, which is a naturally occurring element in the human thyroid gland.

The exhaustive seven-year investigation critically examines the well-established, but likely erroneous, practice patterns of clinician avoidance of administering an iodine-containing contrast agent before imaging tests to patients who believe they have an iodine allergy. A contrast agent or dye is a diagnostic aid that is important for enhancing the visibility of blood vessels and organ systems to help radiologists and other physicians identify irregularities inside the body, such as tumors.

“We could find no documented cases from more than 70 years of research where iodine itself was responsible for patient reactions to iodinated contrast media, amiodarone, povidone-iodine, and other iodine-containing compounds,” said Nicole R. Wulf, PharmD, lead author and FDB clinical pharmacist. “While these patients likely had reactions to the contrast media, iodine was most likely not responsible, nor did most of these reactions meet the definition of an allergic reaction, which requires an immune-mediated reaction such as antibody release and symptoms such as rash, swollen tongue or face, or even difficulty breathing.”

It's reported that 66% to 89% of physicians routinely ask patients prior to an imaging test if they have an iodine allergy or an allergy to shellfish or other seafood that may contain iodine. These self-reported, unverified “iodine allergies” could be based only on a patient’s perceived prior adverse reaction to a contrast agent, or dislike or intolerance to seafood, the latter of which is most likely caused by an animal protein reaction and not iodine.

Determining the precise cause of the patient’s reaction to contrast agents or iodine-containing medications would help ensure they receive the most appropriate imaging and care. Highly targeted medication alerts at the point of ordering could support physicians and patients in understanding the patient’s risks and prompt subsequent allergy testing or an investigation into potential other causes of the allergic-type reaction, according to the authors.

“Another unfortunate consequence of a patient’s self-identified iodine allergy is that it could result in a care delay or a patient receiving unnecessary steroids before an imaging test, which could cause harm,” said study co-author Joan Kapusnik-Uner, PharmD, FASHP, FCSHP, who is FDB vice president of clinical content. “Instead, physicians and patients could determine the specific type of contrast media to which they had an adverse reaction in the past and explore options to avoid that or similar ingredient formulations, or if the reaction was actually due to another cause, such as an interaction with another medication or dehydration.”