Written by Kimiko Dunbar
Spoon Feed
The PEN-FAST clinical decision rule, a penicillin allergy decision rule developed for adults, can help identify pediatrics patients who are at low risk for true allergy. Patients with a score less than 3 may be suitable for oral drug challenge.
Is that rash real or fake news?
Evidence shows that over 90% of people labeled with a penicillin allergy are not truly allergic. In the pediatric population, inappropriate labeling is even more common given challenges distinguishing between allergic reaction and viral exanthem. This retrospective single-center cohort study assessed the utility of the PEN-FAST clinical decision rule (a calculator developed for adults, see graphic below) for penicillin allergy in 700 children aged 6–18 years with suspected hypersensitivity. Confirmed allergy was found in only 9.1% of cases; all true-positive patients had a PEN-FAST score ≥3. This threshold yielded 100% sensitivity (95%CI 0.94–1.00), 45% specificity, and AUC of 0.73. Limitations include retrospective design and limited generalizability. PEN-FAST may have utility in identifying low-risk pediatric patients suitable for oral challenge of penicillin.
How does this change my practice?
I like that the PEN-FAST clinical decision rule facilitates objective clinical decision-making by generating a numeric score; however, I could imagine some patients with mild reactions receiving a score of 3 simply for having had the reaction in the past 5 years and receiving some cetirizine for perceived itching. We do a fair amount of penicillin delabeling in the hospital where I work––giving a test dose under close monitoring with epi at the bedside. This scoring system will provide me peace of mind for the kids I’m challenging with a PEN-FAST <3!
Source
PEN-FAST in pediatrics: a reliable tool for penicillin allergy assessment? Eur J Pediatr. 2025 Jul 2;184(7):463. doi: 10.1007/s00431-025-06305-3. PMID: 40601050
