D3.50 - Penicillin-allergic labelled patients with a PEN-FAST score of 0 could safely be de-labelled by non-allergists

Penicillin allergy is often over-diagnosed, with around 10% of individuals labelled as allergic, but only 1% actually being allergic. De-labelling unnecessary penicillin allergy diagnoses is essential for optimizing treatment. PEN-FAST is a simple tool to identify patients at low risk for a true penicillin allergy. We aimed to assess the proportion of patients with a PEN-FAST score of 0 and whether they can safely receive penicillin under the supervision of non-allergists.

In this retrospective, single centre study we included patients who underwent formal penicillin allergy testing at University Clinic Golnik. The PEN-FAST score (0-5) was calculated for each patient. Patients were tested first with a skin test and skin test negative patients underwent an oral provocation test. Data were collected from January 2024 to March 2024.

The primary outcome for the model was any positive result of penicillin allergy testing.

The patient cohort had 221 patients (160 female (72.4%)). A cut-off of 0 points for PEN-FAST was chosen to classify a low risk of penicillin allergy. 44.1% had a PEN-FAST score of 0, 8.1% had a score of 1, 36.5% a score of 2, 3.6% a score of 3 and 4 – 4.1% had a score of 5. 25 patients (11.3%) tested positive for a penicillin allergy. 22 (88%) of patients with a positive allergy test had a PEN-FAST score above 0. 3 (12%) patients that tested positive for a penicillin allergy and had a PEN-FAST score of 0 had a mild skin reaction only after the penicillin testing and none required treatment. 101 (51.5%) patients with no proven penicillin allergy had a PEN-FAST score above 0.

The sensitivity to identify penicillin allergy was 88%, specificity 48%, PPV 17% and high NPV of 96%.

We observed that 44% of patients who were referred to penicillin allergy testing had a PEN-FAST score of 0. PEN-FAST 0 had a high negative predictive value of 96%, and the reactions in patients with this score were mild. Our results suggest that patients with a PEN-FAST score of 0 could safely be identified by non-allergists as low-risk for penicillin allergy and prescribed penicillin without the need for further allergological workup. This approach could significantly alleviate the burden on allergy clinics.