Development and validation of a penicillin allergy clinical decision rule
Trubiano JA, Vogrin S, Chua KYL, et al. JAMA Intern Med. 2020;180(5):745-752.
Self-reported penicillin allergies not only limit antibiotic choices for some patients but also affect antibiotic-stewardship programs and antibiotic-resistance patterns.
Restricting antibiotic choices may be worthwhile if an allergy is real, but many self-reported penicillin allergies are actually nonexistent (10% of self-reported penicillin allergies are confirmed, according to best estimates).
Some facilities have incorporated antibiotic-allergy testing (AAT) programs into real-time patient care, which have resulted in high rates of posttest ability to use beta-lactams.
However, AAT requires time and specialist interpretation, and it is labor intensive.
The authors of this article attempt to develop a point-of-care decision rule. They enrolled a prospective cohort of patients undergoing AAT who were recruited between May 2015 and June 2019.
Data for patients who reported any penicillin allergy and underwent skin-prick testing, intradermal testing, patch testing, and/or oral challenge (directly or after skin testing) were extracted from a prospective database.
The internal validation cohort included 622 patients (median age 60; 59% female), and the prevalence of a positive penicillin allergy test was 9.3%.
The 4 features associated with a positive result in the penicillin allergy test through multivariable analysis can be summarized by the mnemonic PEN-FAST (penicillin allergy: 5 or fewer years since the last reaction [2 points], anaphylaxis/angioedema or severe cutaneous adverse reaction [2 points], and treatment required for an allergy episode [1 point]).
The scoring system is as follows: 0 = very low risk of positive penicillin allergy test (<1%); 1 or 2 = low risk (5%); 3 = moderate risk (20%); and 4 or 5 = high risk (50%).
Using a cutoff of <3 points had a sensitivity of 70.7%, a specificity of 78.5%, a PPV of 25.3%, and an NPV of 96.3% (a PEN-FAST score of 0 had an NPV of 99.4%).
The rule was then validated among 945 patients from 3 sites (Sydney, Perth, and Nashville). The test characteristics were highly similar to those of the derivation cohort.
Even if a patient is at low risk, the authors are not advocating for immediately giving IV penicillin or discharging patients with a prescription; instead, they recommend performing an observed oral challenge.
EDITOR’S COMMENTARY: The authors developed a clinical decision rule to identify patients who are at low risk of having true penicillin allergy (PEN-FAST). The rule includes 4 elements: (1) penicillin allergy, (2) 5 or fewer years since the last reaction (2 points), (3) anaphylaxis/angioedema or severe cutaneous adverse reaction (2 points), and (4) treatment required for an allergy episode (1 point). A score <3 had excellent NPV, but further validation in diverse patient populations will be required before this rule is used at the bedside in the ED.
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