Penicillin skin testing in the management of penicillin allergy in an outpatient pediatric population

Background: Eight to ten percent of patients believe that they are allergic to penicillin, yet only 10% of those patients have evidence of an immunoglobulin E (IgE) mediated allergy upon penicillin skin testing (PST). In the adult population, a negative PST result is associated with a low risk of immediate reaction on oral challenge, but further studies are needed in the pediatric population. Objective: To calculate the negative predictive value (NPV) of the current skin testing regimen of penicillin, benzylpenicilloyl-polylysine (the major determinant), and ampicillin in a pediatric outpatient population to assess the utility of adding the minor determinant mixture to the skin testing regimen. Methods: A retrospective chart review was conducted of all pediatric patients seen in a single-center pediatric allergy/immunology outpatient clinic between January 1, 2010, and March 1, 2016, who underwent PST for presumed penicillin drug allergy. Results: Only 38% of patients who underwent PST had a drug reaction history consistent with an IgE-mediated reaction. 28.8% of the patients had a positive PST result. The addition of ampicillin to the standard PST regimen of penicillin and benzylpenicilloyl-polylysine identified an additional 4.1% of patients. Two patients (3.2%) reacted on oral challenge with a minor rash. The NPV of the PST regimen was 98%. No significant predictive variables for a positive PST result were identified. Conclusion: Given the high NPV of the current PST regimen, we do not recommend additional testing with the minor determinant mixture. Despite this high NPV, the utility of PST in the low-risk, low-pretest probability outpatient pediatric population was limited, and select patients may be able to proceed directly to oral challenge.