Utility of fresh egg skin prick test and egg yolk specific immunoglobulin E for outgrowth.

Background: In children younger than 2 years, studies evaluating the value of skin prick tests (SPTs) and specific immunoglobulin E (sIgE) results to predict persistence or resolution of egg allergy (EA) are limited. In addition, the value of egg yolk (EY) sIgE and fresh egg (FE) SPTs has not been well characterized.

Objective: To investigate the optimal decision points (ODPs) for outgrowing allergy with SPTs and sIgE tests for egg allergen preparations.

Methods: SPTs for FE, egg white (EW), and EY, sIgE tests for EW and EY, and oral food challenges (OFCs) were performed in children with suspected EA. Reactive patients strictly avoided all dietary egg. After 1 year, EA was reevaluated with addition OFCs, SPTs, and sIgE tests.

Results: A total of 81 children (median age, 7 months; age range, 2-24 months) were enrolled. Notably, 4 children with a history of anaphylaxis and 60 of 77 children with a positive challenge result underwent egg elimination. The 1-year follow-up OFC test was performed on 59 children. A total of 27 reacted to egg. No persistent patient had a follow-up SPT result for FE of 4 mm or less (positive predictive values of 100% and negative predictive value of 56% for outgrowth). The diameters of the initial SPT for FE decreased 50% or more in half of the patients who outgrew EA. The ODPs for outgrowing allergy for follow-up sIgE tests for EY and EW were 2.1 kU/L or less (positive predictive value of 86.2%) and 4.0 kU/L or less (positive predictive value of 84.6%), respectively.

Conclusion: A SPT diameter for FE of 4 mm or less and sIgE values of 2.1 kU/L or less for EY and 4.0 kU/L or less for EW have a good positive predictive value for outgrowth of EA in children younger than 2 years.