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BackgroundAdverse drug reactions to iodinated contrast media (ICM) have risen due to their increasing use in x‐ray‐based imaging modalities. Delayed hypersensitivity reactions are mainly caused by nonionic monomeric compounds and represent an issue impacting the diagnostic–therapeutic pathways of cancer, cardiology and surgery patients.ObjectivesTo prospectively evaluate the usefulness of skin tests in delayed hypersensitivity reactions to ICM and to evaluate the tolerability of iobitridol, a monomeric nonionic low osmolality compound, as a possible safe alternative.MethodsPatients with delayed hypersensitivity reactions to ICM referred to us from 2020 to 2022 were prospectively enrolled in the study. All patients underwent patch test and, if negative, intradermal test with the culprit ICM and iobitridol as alternative.ResultsA total of 37 patients (females 24, 64.9%) were enrolled in the study. Iodixanol and iomeprol were the most frequently involved ICM (48.5% and 35.2%, respectively); 62.2% of patients presented maculopapular eruption, while 37.8% reported delayed urticaria‐like rash. Skin tests resulted positive to the culprit ICM in 19 patients (51.4%), 16 to patch test and 3 to intradermal test. Skin tests with iobitridol, tested as alternative, resulted positive in 3/19 patients (15.8%). All 16 patients with negative results to iobitridol were administered this ICM and tolerated it.ConclusionsIn at least half of patients, delayed‐type hypersensitivity was demonstrated by skin tests, particularly by patch test. This diagnostic approach resulted simple, cost‐effective and safe, not only to confirm the culprit ICM but also to identify iobitridol as feasible alternative.

the site of contact but can develop into a generalized dermatitis. 15 The sensitizing properties of acetophenone azine have been confirmed. 16 Strong suspicion is necessary to diagnose allergy to acetophenones as commercial patch test preparations are not available. Patch testing with patient's own products is essential before further investigation. An optimal concentration for testing resacetophenone would appear to be 0.1% in petrolatum. The degree of cross-reactivity is unknown.