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Validation of the PEN-FAST Penicillin Allergy Clinical Decision Rule in an Asian Cohort
Xin Rong Lim1, Ryan Xuan Wei Teo1, Justina Wei-Lyn Tan1
1Department of Rheumatology, Allergy and Immunology, Tan Tock Seng Hospital, Singapore, Singapore.
Introduction:
A false penicillin allergy label often leads to the unnecessary avoidance of beta-lactam antibiotics, contributing to antimicrobial resistance and suboptimal clinical outcomes. The PEN-FAST clinical decision rule is a simple, point-of-care tool with a high negative predictive value (NPV) designed to identify low-risk patients who may not require extensive allergy testing. This study aims to validate the performance of the PEN-FAST clinical decision rule in an Asian population.
Methods:
A retrospective review of medical records from January 2006 to February 2023 was conducted at our institution's outpatient allergy clinic. Patients underwent skin prick and intradermal testing, followed by oral drug provocation testing (DPT) or direct oral DPT without prior skin testing (ST). Positive results were defined as positive skin test outcomes or immediate/delayed reactions following drug challenge. PEN-FAST scores were compared to allergy testing results.
Results:
A total of 357 patients were included, with 85 (23.8%) undergoing direct DPT without prior ST. None had a history of severe cutaneous allergic reaction as their index reaction. The median age was 49 years (interquartile range [IQR]: 34-63), and 61.9% were female. Forty-seven patients (13.2%) had positive test results, including 26 positive reactions following DPT. PEN-FAST scores of 0-5 were distributed as follows: 25 (7.0%), 159 (44.5%), 31 (8.7%), 96 (26.9%), 4 (1.1%) and 42 (11.8%). Among those with PEN-FAST scores ≤ 2 (n = 215), 16 (7.4%) had a positive test. Of these, 7 developed urticaria, 8 developed mild delayed maculopapular exanthem and 1 had a positive skin test. A PEN-FAST score cutoff of ≤ 2 yielded sensitivity of 66.0% (95% CI: 50.7%-79.1%), specificity of 64.2% (95% CI: 58.6%-69.5%), a positive predictive value (PPV) of 21.8% (95% CI: 17.8%-26.5%) and a NPV of 92.6% (95% CI: 89.2%-94.9%). The area under the receiver operating characteristic curve was 0.66 (95% CI: 0.58-0.75).
Conclusion:
The PEN-FAST clinical decision rule demonstrates a high NPV in an Asian population, supporting its potential utility in identifying individuals unlikely to have true penicillin allergy and enabling direct DPT in low-risk patients without prior ST. However, the modest area under the curve (AUC) of 0.66 reflects limited overall discriminatory ability.
