PEN-FAST Score Calculator

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PEN-FAST Calculator

PEN-FAST (Penicillin Allergy Decision Rule)

Estimates likelihood of a positive penicillin allergy test based on history (score 0–5).

F — Five years or less since reaction (2 points)
A/S — Anaphylaxis/Angioedema OR SCAR (2 points)

SCAR = severe cutaneous adverse reaction (e.g., SJS/TEN, DRESS). If you’re unsure, choose “No/Unknown”.

T — Treatment required for reaction (1 point)

Any treatment given for the reaction (e.g., antihistamine, steroids, epinephrine, ED visit treatment).

Score: — / 5
Complete the form to calculate.
This tool is for education/decision support and does not replace clinician judgment. Avoid using oral challenge pathways when there is a history suggestive of SCAR or severe reaction; refer to allergy specialists/local guidance.

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