Symptom-based prevention strategy for delayed contrast reactions

Published online August 1, 2025

Iodinated contrast media (ICM) can sometimes cause delayed allergic-like reactions that appear hours to days after the scan. While immediate reactions to ICM are well studied, there has been little clear, evidence-based guidance on how to prevent recurrences of delayed reactions when patients need another contrast study. 

In a recent study published in The Journal of Allergy and Clinical Immunology: In Practice, Jeong and Kim et al. examined practical prevention steps and whether the most effective strategy depends on clinical features of the first reaction. An 11-year cohort study at a tertiary center included patients with a history of a delayed reaction to ICM who subsequently underwent additional contrast-enhanced imaging. The authors compared recurrence rates after two common strategies: (1) switching to an alternative ICM with a different chemical side-chain and (2) premedication (an antihistamine with or without corticosteroid). They analyzed outcomes overall and by the clinical pattern of the first reaction—itching/hives/angioedema versus maculopapular rash—and by onset timing (accelerated, 1–6 hours; delayed, >6 hours). 

Recurrence per exposure was low overall, but notably about 40% of recurrences happened within the first hour after re-exposure—highlighting the importance of early post-contrast observation even in patients with a prior delayed reaction. For patients whose initial reaction involved itching, hives, or angioedema, two measures independently reduced risk: switching to an ICM with a different side-chain and taking an antihistamine before the scan. For those with a maculopapular rash, simply changing to an alternative ICM reduced recurrence with no additional benefit from premedication; steroid-containing regimens did not outperform antihistamine alone. Together, these findings support a symptom-based approach: (a) itching/hives/angioedema patients should use a different-side-chain agent ± antihistamine; (b) maculopapular rash patients should change the agent regardless of common side chain; and (c) in all cases, ensure early observation after re-exposure.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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