Allergological Work‐Up in Cephalosporin Allergy Diagnosis and Delabelling: The Experience From Two European Allergy Centres

Background Diagnostic strategies for cephalosporin allergy are not well defined due to differences in inclusion criteria among studies and a lack of standardised diagnostic tests. Our aim was to describe the characteristics of patients with a suspicion of cephalosporin allergy and to analyse the role of in vivo tests. Methods Patients with suspected cephalosporin allergy were prospectively evaluated (2019–2023). Diagnosis was achieved using clinical history, skin tests ( STs ) and, if negative, drug provocation tests ( DPTs ). A randomised group of patients who tolerated DPT were retested by STs at 2–8 weeks. Results 211 patients were evaluated, with 55.4% reporting IRs and 44.5% NIRs . Skin was involved in half of the patients reporting IRs and in all reporting NIRs ( p < 0.0001). Anaphylaxis was experienced by 18% and shock by 7.1%. The cephalosporin most commonly involved was cefuroxime (63.6%) ( p < 0.0001) in the Spanish cohort and cefazolin (51%) ( p < 0.0001) in the Italian one. Allergy was confirmed in 57.2% of patients reporting IRs (47% by STs and 9.4% by DPT ) and 14.9% of NIRs (5.3% by STs and 8.5% by DPT ). In the positive‐ ST group, the percentage of grade II and III reactions was higher ( p = 0.02) and the interval reaction‐study shorter ( p = 0.0007) than in negative‐ ST . Of the 48 patients retested, 1 (2.9%) who reported an IR and 1 (7.1%) who reported NIR resulted positive. Conclusions The patterns of cephalosporin allergy may differ across different regions, being STs and DPT useful for diagnosis. Further studies are needed to confirm the role of retesting, as well as to identify which patients would benefit most from this procedure.