D2.17 - Diagnostic profitability of penicilloyl-polylysine and minor determinant mixture in urgent/preferred beta-lactam allergy studies in hospitalized patients from january 2023 to december 2025

Penicilloyl-PolyLysine (PPL) and Minor Determinant Mixture (MDM) are reagents for beta-lactam skin testing to accurately diagnose IgE-mediated allergy. However, PPL and MDM are not useful for delayed reactions or for selective reactions to penicillins with unique side chains. Medical histories of beta-lactam allergy in hospitalized patients are often incomplete, with imprecise descriptions of the type of reaction (immediate or delayed), the time of onset, and even the antibiotic involved. This study aimed to investigate diagnostic profitability of PPL and MDM in urgent/preferred beta-lactam allergy studies in hospitalized patients of our hospital.

This was a retrospective observational study. Interconsultations of hospitalized patients from January 2023 and December 2025 were reviewed. The patients referred a history of unconfirmed Beta-lactam allergy and they underwent skin testing as part of the urgent/preferred study. 

Epidemiological data (age and sex), clinical presentation compatible with allergic condition and results of skin tests and controlled exposure test were collected. Skin tests were performed according to our unit's protocol, which includes penicillin, amoxicillin-clavulanic acid (AC), cefuroxime, PPL and MDM.  

We enrolled 70 patients (31 F/ 39 M, median age 71, range 21-93). The results were classified into two groups of patients according to clinical presentation that are presented in a comparative table. Table 1. 

Most patients presented a clinical no compatible with allergic condition (61%). Two patients tested skin tests positive for AC, both with clinical compatible with allergic condition. Only one patient tested positive for PPL (negative for the rest), but the controlled exposure test with cefuroxima was negative. Approximately 80% of patients in both groups underwent a controlled exposure test. There were 3 positive cases in the group of patients with clinical compatible with allergic condition and none in the other group.

Based on our study, the skin tests with PPL and MDM do not provide diagnostic profitability, especially in patients who presented a clinical picture inconsistent with allergy. Therefore, PPL and MDM could be omitted in the urgent/preferential study of beta-lactam allergy in those patients.