ToolsCalculators
Penicillin Allergy Decision Rule (PEN-FAST)
Point-of-care risk stratification of a patient-reported penicillin allergy.
Penicillin Allergy Decision Rule (PEN-FAST)
Five years or less since the reaction (or unknown timing)
Reaction phenotype
Treatment was required for the reaction (or unknown)
Result0 points
Very low risk of a positive penicillin allergy test (<1%). A score <3 was used to identify patients suitable for direct oral challenge without formal skin testing.
When to use
- An adult reporting a penicillin allergy, to decide whether formal allergy testing is needed before de-labeling or safe beta-lactam use.
Formula
PEN-FAST = 5 years or less since reaction (2) + anaphylaxis/angioedema or SCAR (2) + treatment required for the reaction (1). Range 0-5. 0 = very low risk (<1%), 1-2 = low risk (~5%), 3 = moderate risk (~20%), 4-5 = high risk (~50%).
Pearls and pitfalls
- Derived and validated in adults ≥16 years; not validated for non-penicillin beta-lactam allergies alone.
- A cutoff <3 gave an NPV of 96.3% for excluding true penicillin allergy in the derivation/validation cohorts.