Although intravenous (IV) radiocontrast is a vital tool for enhancing imaging in diagnostic procedures, there have been concerns regarding allergic reactions. A 2012 article discusses the possibility of individuals with a previous allergic reaction to seafood (e.g., shellfish) also demonstrating an allergic reaction to contrast media due to the presence of iodine in both. Notably, it is suggested that certain proteins, rather than iodine, act as triggers for patients with seafood allergic reactions. Thus, despite the fact that iodine may be present in contrast media, iodine may not be the true cause of allergic reactions. It has been shown that contrast media causes no immunoglobulin E-related reaction, the true allergic reaction by definition, in vivo. [1]
The 2020 American Society of Emergency Radiology guidelines describe the use of IV contrast for both computed tomography (CT) and magnetic resonance imaging (MRI), with a focus on safety. While the authors address the risk of allergic reactions caused by the use of IV contrast, the association between these reactions and an “iodine allergy” was essentially considered to be a fallacy. As such, the guidelines did not report a need for premedication or special precautions in patients with a history of iodine allergies. Allergic reactions to IV contrast are due to activation of mast cells or basophils, while iodine is found naturally in the human body and is not considered to be an allergen. Gadolinium is an alternative IV contrast agent used in MRI. Initially considered to be very safe, more recently gadolinium has been associated with nephrogenic systemic fibrosis (NSF), a potentially debilitating and fatal multi-organ sclerosing disease. [2]
A 2021 review article describes the current evidence on iodine-containing compounds and the concept of iodine allergy, specifically examining cross-reactivity concerns that may impact patient care. A total of 81 articles were included in the review, which evaluated whether iodine could be confirmed as an allergen. The iodine-containing compounds assessed included iodinated contrast media (ICM), povidone-iodine, potassium iodide, radioiodine, indocyanine green (ICG), and shellfish/seafood. Regarding findings specific to ICG, one study suggested that reactions to ICG are likely due to nonimmunologic histamine release rather than an antigen-antibody response. The review identified three case reports on ICG, though these reports did not provide conclusive evidence. One case involved hypotension after ICG injection in a patient with an ICM allergy who later tolerated ICG, while another described a woman who developed urticaria after intravenous ICG, with skin prick tests for sodium iodide returning negative results. Overall, the authors concluded that iodine has not been proven to be the allergen responsible for reactions to iodinated contrast media, amiodarone, povidone-iodine, or other iodine-containing compounds; however, further details regarding cross-reactivity of ICG in patients with iodinated contrast allergies were not provided. [3]