The term “iodine allergy” is regularly used as a collective denomination to explain adverse reactions to iodine, ranging from seafood allergies to reactions to iodine-based medical X-rays or other medical interventions. In fact, it’s common for people to think that is the iodine in seafood that is the cause of their allergy, but this is not correct.
Even amongst the medical profession, there is confusion regarding seafood allergy, sensitivity to iodinated injections before certain medical examinations and the role of iodine. Iodine allergy should only be used to refer to reactions experienced by patients that received an injection containing contrast dyes containing iodine to improve X-ray images. Its use is widespread in radiology and can be injected almost anywhere in the body. For the majority of the population they are safe, however, in certain patients, it can cause an anaphylatic shock within minutes after administration, with symptoms ranging from mild to severe or life-threatening.
Symptoms, diagnosis and prevention
Unfortunately, as there are no tests currently available, it’s impossible to determine with 100% accuracy whether each patient is going to experience a reaction or not. However, doctors are aware that certain conditions may increase the chances of anaphylactic shock, including those that experienced reactions in previous medical exams and people with asthma, allergies, heart disease or kidney disease, those taking beta-blockers, females and the elderly. In these cases, they may recommend the use of premedication consisting of corticosteroids and antihistamines, but this only seems to be effective in cases with mild to moderate symptoms.
Less dangerous symptoms include skin rash, itching, nasal discharge, nausea and vomiting, occur in 5-8% of people receiving treatment, and generally don’t need treatment. Moderate symptoms include facial or throat swelling, difficulty breathing and irregular heart beats, occur in 1% of people receiving treatment and may need some medical attention.
The more severe symptoms can be life-threatening and include anaphylactic shock, arrhythmias, low blood pressure, throat and lung swelling and seizure, occur in 0.1% of people and need medical treatment. Deaths are extremely rare, and in more than 337,000 patients in a controlled study, only 2 deaths occurred.
Is iodine allergy a real allergic reaction?
The simple answer is no, and it should really be called “allergy-like,” or “pseudo-allergic,” rather than “allergic”. Although, it was originally believed that it was an allergic reaction to the presence of iodine, attempts to produce antibodies have failed. Furthermore, if a patient experiences a reaction to iodine in one treatment there’s only 8-25% chance it will happen again in any subsequent treatments. If this was a true allergy recurrence would be 100%.
Proposed mechanism suggests that histamine and serotonin are released, activating non-specific mediators, marking the beginning of a series of events that will eventually result in the symptoms observed. Iodine can also cause non-anaphylactic reactions, which has been attributed to free iodine, causing iodine mumps. It’s believed this is due to overload of normal pathways of iodide metabolism, and in contrast to allergy responses is dose-dependent.
Iodine intolerance and seafood allergy are not the same thing!
Majority of people suffering from seafood allergies believe it’s due to the high iodine content in these foods. However, there is no connection between iodine allergy and sea food, and just because iodine is found in prawns and shellfish, it doesn’t mean it’s the offender. In fact, the mechanisms causing these reactions are different, going from activation of non-specific immune mediators in the case of iodine allergy to IgE-mediated sensitivity to fish protein in the case of seafood intolerances. Having said that, patients with a seafood allergy may be more prone to a reaction to iodine injection, but the same applies to other food allergies. Furthermore, 85% of patients with seafood allergy experience no adverse reaction.
The term “iodine allergy” to describe both seafood allergies and reaction to iodine-based medical treatments is incorrect and unfortunate, perpetuating confusion both in the general population and even amongst the medical professional. It should therefore be replaced by more neutral descriptive terms such as “iodine sensitivity” and “seafood intolerance or allergy”.
Furthermore, a history of seafood allergy shouldn’t be a contraindication to the use of iodinated contrast media no more than in patients with heart or kidney disease. Patients should be assessed for different factors which may provoke the reaction and the decision to go ahead with these treatments done accordingly, including premedication or, in high risk patients, use of alternative methods, such as gadolinium-based injections.
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