Clinical Question

Which adult patients with a history of penicillin allergy will have positive allergy testing?

Bottom Line

A label of penicillin allergy clears the shelves of many effective treatments for various infections. A simple rule outlined in the synopsis effectively identifies (without allergy testing) low-risk penicillin allergies in patients with a history of a penicillin allergy event. (Level of Evidence = 1a)

Synopsis

The PEN-FAST rule was developed using a group of 622 patients with a history of reacting to penicillin who were referred for allergy testing, and then validated on a second group of 945 patients who were referred for allergy testing at three other sites. Allergy testing consisted of skin prick, intradermal, or patch testing, with a positive test confirmed by oral challenge. In the validation group, 27.4% reported a history of angioedema and/or anaphylaxis. Following testing in this group, the prevalence of reacting to any allergy test was 9.9%, but only 21 participants reacted to the oral challenge (2.2%). For patients who report a PENicillin allergy, here is the FAST rule:

• F (five years or less since the reaction): 2 points

• A (anaphylaxis or angioedema) or S (severe cutaneous reaction): 2 points

• T (treatment required for reaction): 1 point

Patients with a score of 0 had a likelihood of a positive test result of less than 1%; a score of 1 or 2 yielded a positive test result in 5%. Among the three cohorts, sensitivity ranged from 70.4% (prevalence 27%) to 87.5% (prevalence 14.4%).

Study design: Decision rule (validation)

Setting: Outpatient (any)

Reference: Trubiano JA, Vogrin S, Chua KYL, et al. Development and validation of a penicillin allergy clinical decision rule. JAMA Intern Med. 2020;180(5):1–9.

Editor's Note: Dr. Shaughnessy is an assistant medical editor for AFP.