The Combined Use of Chronological and Morphological Criteria in the Evaluation of Immediate Penicillin Reactions: Evidence From a Large Study

BACKGROUND: Immediate hypersensitivity reactions to penicillins are often labeled on the basis of a similar set of symptoms, but a key feature of these reactions that can be reproduced in diagnostic testing may be the timing of a reaction in relation to the dose administration. OBJECTIVE: To determine whether the timing of a reaction in response to the last dose of a penicillin would predict the results of diagnostic testing. METHODS: We evaluated 1074 patients by performing skin tests, serum specific IgE assays (ImmunoCAP), and challenges. Patients who were evaluated by us more than 6 months after their reactions and found negative were reevaluatedwithin 2 to 4 weeks. RESULTS: Patients who had reacted within 1 hour after the first dose, within 1 hour after subsequent doses, more than 1 hour to within 6 hours after the first dose, or more than 1 hour to within 6 hours after subsequent doses were classified as group A (758 individuals), B (92), C (67), or D (157), respectively. Penicillin hypersensitivity was diagnosed in 707 patients ( 65.8%) by skin tests (407 patients, 57.6%), ImmunoCAP (47, 6.6%), both tests ( 232, 32.8%), or challenges (21, 3%). A conversion to allergy- test positivity occurred in 7 of 10 patients with anaphylactic reactions and in 1 of 28 patients with other reactions who were reevaluated after negative challenges. The rate of penicillinallergic patients in groups A, B, C, and D was 85%, 35.9%, 35.8%, and 3.8%, respectively. Only 1 of 107 patients reporting cutaneous reactions lasting more than 1 day had positive results to allergy tests. CONCLUSIONS: IgE-mediated hypersensitivity can be diagnosed by skin tests in about 70% of subjects who react within 1 hour (eg, patients from groups A and B). This hypersensitivity can be lost over time, as demonstrated by the negativization of allergy tests in follow-up studies. In subjects with anaphylactic reactions, however, it is advisable to not consider this phenomenon definitive. In fact, a conversion to allergy test positivity can be observed in up to 20% of such subjects retested after negative challenges. (c) 2022 American Academy of Allergy, Asthma & Immunology

Automated summary

The timing of a reaction in response to the last dose of a penicillin can predict the results of diagnostic testing. IgE-mediated hypersensitivity can be diagnosed by skin tests in about 70% of subjects who react within 1 hour. However, this hypersensitivity can be lost over time.