Validity of PEN-FAST as a clinical decision tool in pregnant patients.

Background: Reported penicillin allergies are associated with adverse patient outcomes, particularly in high-risk patient states such as pregnancy. The PEN-FAST clinical decision-making tool has previously been validated in general populations to identify individuals at low risk for penicillin allergy. Objective: We aimed to validate PEN-FAST in risk-stratifying-reported penicillin allergies in pregnant patients to enhance delabeling. Methods: Between September 2020 and June 2023, pregnant patients with reported penicillin allergies underwent allergy evaluation in Yale New Haven Hospital-affiliated allergy and immunology clinics. We retrospectively calculated PEN-FAST scores of pregnant patients who had undergone skin testing and/or oral challenge. Sensitivity, specificity, positive predictive value, negative predicative value, area under the curve, and positive and negative likelihood ratio were calculated for each PEN-FAST score (0-5). Results: Penicillin allergy testing was performed on 334 patients with a mean age of 32.2 plus or minus 4.6 years and a mean gestational age of 31.7 plus or minus 4.7 weeks (range 16.4-39.3 weeks). A total of 326 patients underwent oral challenge. All passed the testing and were delabeled. A PEN-FAST cutoff of 2 or lower showed a specificity of 93.1% (95% CI = 89.8-95.6) and a negative predictive value of 99.7 (95% CI = 98.2-100.0). Conclusion: PEN-FAST can be used to improve risk stratification of reported penicillin allergies among pregnant patients, enhancing delabeling in this population. Our data also support the idea that skin testing and oral challenge are well tolerated at a wide range of gestational ages as young as 16 weeks. In our large cohort of more than 300 pregnant patients, the majority were low-risk and all who underwent oral challenge passed without any severe adverse events.