Calculators · Infectious Diseases · Score
PEN-FAST penicillin allergy rule
Also called PEN FAST, penicillin allergy decision rule
Point-of-care risk that a patient-reported penicillin allergy is a true allergy on testing.
PEN-FAST
0 / 5
- Band
- Very low risk
- Positive allergy test (derivation)
- 0.6%
Very low risk: about 0.6% had a positive penicillin allergy test in the Australian derivation cohort. A score below 3 had a negative predictive value of 96.3%; the authors propose such allergies may not need formal skin testing.
Formula and scoring
Applies to a patient reporting Penicillin allergy. Five or fewer years ago (2) + Anaphylaxis/angioedema or Severe cutaneous reaction (2) + Treatment required (1). <3 = low risk.
Exam and ward pearls
- Score <3 classifies a low-risk penicillin allergy (NPV 96.3%).
- Mnemonic: PEN (penicillin allergy reported), Five or fewer years, Anaphylaxis/angioedema, Severe cutaneous reaction, Treatment required.
When not to rely on it
- Derived in tertiary Australian adults with external validation in Australia and the US; not validated in children.
- Does not replace allergist assessment for severe delayed reactions.
Source
- Trubiano JA, Vogrin S, Chua KYL, Bourke J, Yun J, Douglas A, et al. Development and validation of a penicillin allergy clinical decision rule. JAMA Intern Med. 2020;180(5):745-52. doi:10.1001/jamainternmed.2020.0403 · PMID 32176248
Formula and cut-offs checked against these sources on 8 Nov 2026. Educational tool for clinicians; it does not replace clinical judgement.