Detection of Serum‐Specific IgE by Fluoro‐Enzyme Immunoassay for Diagnosing Type I Hypersensitivity Reactions to Penicillins

Abstract

Diagnosis of type I hypersensitivity reactions (IgE‐mediated reactions) to penicillins is based on clinical history, skin tests (STs), and drug provocation tests (DPTs). Among in vitro com-plementary tests, the fluoro‐enzyme immunoassay (FEIA) ImmunoCAP® (Thermo‐Fisher, Wal-tham, MA, USA) is the most widely used commercial method for detecting drug‐specific IgE (sIgE). In this study, we aimed to analyze the utility of ImmunoCAP® for detecting sIgE to penicillin G (PG) and amoxicillin (AX) in patients with confirmed penicillin allergy. The study includes 139 and 250 patients evaluated in Spain and Italy, respectively. All had experienced type I hypersensitivity reactions to penicillins confirmed by positive STs. Additionally, selective or cross‐reactive reactions were confirmed by DPTs in a subgroup of patients for further analysis. Positive ImmunoCAP® results were 39.6% for PG and/or AX in Spanish subjects and 52.4% in Italian subjects. When only PG or AX sIgE where analyzed, the percentages were 15.1% and 30.4%, respectively, in Spanish pa-tients; and 38.9% and 46% in Italian ones. The analysis of positive STs showed a statistically significant higher percentage of positive STs to PG determinants in Italian patients. False‐positive results to PG (16%) were detected in selective AX patients with confirmed PG tolerance. Low and variable sensitivity values observed in a well‐defined population with confirmed allergy diagnosis, as well as false‐positive results to PG, suggest that ImmunoCAP® is a diagnostic tool with relevant limita-tions in the evaluation of subjects with type I hypersensitivity reactions to penicillins.