The following is the summary of “Combined Use of Chronological and Morphological Criteria in the Evaluation of Immediate Penicillin Reactions: Evidence From a Large Study” published in the December 2022 issue of Allergy and Clinical Immunology by Romano, et al.

Immediate hypersensitivity reactions to penicillins are typically classified based on a shared set of symptoms. Still, the timing of a reaction in relation to the dose administration may be a critical aspect of these reactions that can be recreated in diagnostic tests. Test whether the timing of a reaction to the final dosage of penicillin may be used to predict the outcome of diagnostic testing. Researchers used skin testing, serum-specific IgE assays (ImmunoCAP), and challenges to assess 1,074 patients. When investigators conducted an evaluation more than 6 months after a patient’s reaction and found unfavorable results, they reevaluated them within 2 to 4 weeks.

Patients were categorized as belonging to group A (758 people), B (92 people), C (67 people), or D (157 people) based on whether their reaction occurred within 1 hour of the first dose, within 1 hour of subsequent doses, more than 1 hour to within 6 hours of the first dose, or more than 1 hour to within 6 hours of subsequent doses. There were 707 patients (65.6%) who were diagnosed with penicillin hypersensitivity using skin tests (407 patients, 57.6%), ImmunoCAP (47 patients, 6.6%), both tests (232 patients, 32.8%), or challenges (21%). 7 out of 10 patients with anaphylactic reactions and one out of 28 patients with other reactions who were reevaluated after negative challenges had their allergy tests become positive. About 85% of patients in Group A patients, 35.7% of Group B, 35.7% of Group C, and 3.8% of Group D were penicillin-allergic. 

Allergy tests were only positive in 1 of 107 patients who reported a cutaneous reaction lasting longer than 1 day. Approximately 70% of people with an immediate skin test reaction can be identified with IgE-mediated hypersensitivity (eg, patients from groups A and B). Allergy tests have become negative over time, proving that this hypersensitivity might fade away. However, this phenomenon should not be taken at face value in people with anaphylactic reactions. When such subjects are retested following negative challenges, as many as 20% show conversion to allergy test positivity.