Iodine Allergy
Sonya Collins
Every year, an estimated 75 million people worldwide require procedures that involve the use of contrast media. Prior to these procedures, the overwhelming majority of physicians—66% to 89%—ask patients about seafood or shellfish allergies based on their perception that iodine triggers those allergies and therefore these patients may not tolerate contrast media. Despite little or no evidence to support the existence of iodine allergies or a link between seafood allergy and iodine-containing products, anywhere from 20% to 75% of physicians say they would halt orders for the radiologic procedures or order premedication of patients due to perceived iodine allergy, according to a recent study published in American Journal of Health-System Pharmacy (AJHP).
“The belief that seafood allergy equates to iodine allergy is the longest-standing complete myth I have ever heard,” says David Stukus, MD, professor of clinical pediatrics, division of allergy and immunology, Nationwide Children’s Hospital in Columbus, OH.
The AJHP study reviews the evidence for iodine as an allergen and for an association between seafood allergy and iodine-containing products and offers guidance for clinicians.
“The main premise for the paper is that iodine is not an allergen,” says Joan Kapusnik-Uner, PharmD, vice president of clinical content at First Databank and senior author of the study. “You may have an allergy to contrast media, but it’s something else in the molecule that’s causing the allergic reaction.”
Study findings
In a review of 81 published articles, the study authors found little or no evidence that iodine or iodide acts as an allergen.
The review also failed to prove that iodine-containing products trigger an allergic reaction in people perceived to have iodine allergy, including seafood allergies.
If a patient has an allergy to contrast media, Kapusnik-Uner says, “it could be an intolerance to something else in the media, such as the hyperosmolarity of the contrast media. Or, for Povidone-iodine, the povidone is actually the allergen.”
Seafood myth
The belief that a seafood allergy amounts to an iodine allergy dates back at least 45 years and seems to have been propagated by physicians themselves.
A 1975 study in the American Journal of Roentgenology assessed patients with a history of adverse reaction to contrast media. As nearly 15% of the patients reported a seafood allergy, the study author concluded that it was iodine in both fish and contrast media that acted as an allergen.
“Fifteen percent said they had chocolate allergies and milk allergies, too, but nobody ever asks if you have a chocolate allergy before you get a CT scan,” Stukus says. “For people who react to shellfish,” he adds, “they have allergic reactions to proteins in the muscle called tropomyosin. It has nothing to do with iodine.”
Worse outcomes in perceived iodine allergy
The AJHP study concludes that perceived iodine allergy among patients and providers may lead to worse outcomes for those patients. Providers may withhold necessary imaging studies altogether or order premedication that may increase costs, hospital stay durations, and delay imaging studies.
Takeaways
When recording patient allergies in charts, it’s important to steer away from naming iodine as the allergen.
“If you’re profiling a reaction, if it’s a contrast media, for example, that’s what you should profile and not say it’s an iodine-containing product,” says Nicole R. Wulf, PharmD, a clinical pharmacist at First Databank and first author on the AJHP study.
On the other hand, Kapusnik-Uner says, “asking patients if they have a seafood allergy before giving them contrast media is probably not a good thing because then if they do, they are not going to get the care they need, which is the MRI or CT scan with contrast.”
Community pharmacists can play an important role in educating patients about the iodine allergy myth. “If pharmacists see ‘iodine allergy’ in patient’s medical records, they can dig into the record to find out what specific product caused the reaction and make things more clear,” Wulf said. The bottom line is that while the existence of an iodine allergy has been debunked in numerous studies, individual clinical practice does not always reflect that.
“Iodine is an essential micronutrient in our body used for the synthesis of thyroid hormones. We shouldn’t be saying anyone has an allergy to iodine so we won’t have those delays in care,” Kapusnik-Uner says. ■