# Implementing PEN‐FAST for penicillin allergy delabeling in a high‐prevalence population

## TL;DR

This study shows that the PEN-FAST score safely identifies patients with a penicillin allergy label who can be safely delabeled without prior skin testing.

## Contribution

The study validates the PEN-FAST score's high negative predictive value and safety in a high-prevalence allergy population.

## Key findings

- 99 out of 149 patients with a penicillin allergy label were successfully delabeled after testing.
- PEN-FAST had a negative predictive value of 95.8% in both retrospective and prospective cohorts.
- Only three low-risk patients were misclassified by PEN-FAST.

## Abstract

Self‐reported penicillin allergies lead to the use of broad‐spectrum antibiotics, increase drug resistance, and constitute an economic burden. The PEN‐FAST score aims to identify low‐risk patients for direct drug provocation tests (DPT) without prior skin testing with a reported negative predictive value (NPV) of over 95%.

In this single‐center study (Department of Dermatology, University Hospital Heidelberg, Germany), the PEN‐FAST score was evaluated for patients carrying a penicillin allergy label between 2004 and 2024. Skin testing, allergen‐specific IgE, and consecutive DPT were performed.

A total of 189 patients were analyzed. In a retrospective cohort, 106 of 149 patients showed negative skin tests and received DPT, leading to the delabeling of 99 patients (66.4%). PEN‐FAST identified 55 of 149 (36.9%) as low‐risk, of which three low‐risk patients were misclassified. In a prospective PEN‐FAST low‐risk cohort, one of 40 patients showed a mild reaction after DPT. Overall, NPVs of both PEN‐FAST and formal allergy testing were 95.8%.

Our results advocate for direct DPT in patients carrying a penicillin allergy label classified as low‐risk by PEN‐FAST. PEN‐FAST demonstrated high NPV, safety, and feasibility in a cohort with a high prevalence of true allergies.