Patient-Oriented Evidence That Matters

Easy Rule Identifies Patients with Low-Risk Penicillin Allergies


Am Fam Physician. 2020 Dec 1;102(11):692-693.

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)


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.

POEMs (patient-oriented evidence that matters) are provided by Essential Evidence Plus, a point-of-care clinical decision support system published by Wiley-Blackwell. For more information, see http://www.essentialevidenceplus.com. Copyright Wiley-Blackwell. Used with permission.

For definitions of levels of evidence used in POEMs, see http://www.essentialevidenceplus.com/product/ebm_loe.cfm?show=oxford.

To subscribe to a free podcast of these and other POEMs that appear in AFP, search in iTunes for “POEM of the Week” or go to http://goo.gl/3niWXb.

This series is coordinated by Sumi Sexton, MD, editor-in-chief.

A collection of POEMs published in AFP is available at https://www.aafp.org/afp/poems.



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