This multicenter retrospective cohort study across 5 EDs (Jan 2022–Dec 2024) evaluated whether timing of IV contrast administration — ≤4 h vs >4 h after premedication (antihistamine + corticosteroid) — affected breakthrough contrast reaction rates in ED patients ≥21 years old with documented iodinated contrast allergy requiring contrast-enhanced CT.
No significant difference in breakthrough reaction rates: 8/279 (3%) in the ≤4-h group vs 3/68 (4%) in the >4-h group (OR 0.66; 95% CI 0.17–2.5; p=0.52). Of 11 total reactions, 6 were mild and 5 were moderate; none were severe and there were no mortalities.
- Retrospective design limits causal inference and is subject to documentation bias. - Small number of total reaction events (n=11) limits statistical power to detect meaningful differences. - Significant imbalance in group sizes (279 vs 68) may reflect selection bias in who received contrast earlier.
In ED patients with iodinated contrast allergy, administering contrast within 4 h of IV premedication appears safe, with reaction rates comparable to longer premedication windows. Clinicians can likely proceed with the ACR accelerated 4-h regimen without added risk, supporting its continued use in time-sensitive ED scenarios.
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