# Diagnostic Utility of Skin Prick Test Ratios and Specific IgE in Predicting Egg White Allergy: Reducing the Need for Oral Food Challenges in Children

## TL;DR

This study finds that absolute skin prick test wheal size and specific IgE levels are better predictors of egg allergy than normalized ratios, helping reduce unnecessary oral food challenges in children.

## Contribution

The study demonstrates that histamine-normalized skin prick test indices do not add value over absolute wheal size in predicting egg allergy outcomes.

## Key findings

- Absolute egg white SPT wheal diameter and serum sIgE are independent predictors of OFC positivity.
- Histamine-normalized indices showed no clear superiority over absolute wheal size in predicting OFC outcomes.
- 21.9% of the 105 children tested had a positive oral food challenge for egg allergy.

## Abstract

Background: Skin prick testing (SPT) and serum egg white–specific IgE (sIgE) support oral food challenge (OFC) decisions in suspected egg allergy, but the incremental value of histamine-normalized SPT indices remains uncertain. Methods: In this single-center retrospective study, 105 egg-sensitized children underwent clinically indicated OFC. Commercial egg white SPT, prick-to-prick testing with fresh egg white, histamine controls, and serum egg white–specific IgE were assessed. Discriminatory performance was evaluated by ROC analysis, and independent predictors of OFC positivity were identified using multivariable logistic regression. Results: OFC was positive in 23 of 105 children (21.9%). Egg white SPT wheal diameter, the prick-to-histamine ratio, and serum egg white–specific IgE (sIgE) levels were significantly higher in OFC-positive patients (all p < 0.001). ROC analysis demonstrated moderate-to-good discrimination for both sIgE (AUC = 0.767) and the prick-to-histamine ratio (AUC = 0.786), without clear superiority of normalized indices. In multivariable logistic regression analysis, only absolute egg white SPT wheal diameter (adjusted OR 1.41 per 1 mm increase; 95% CI 1.13–1.77) and serum egg white–specific IgE level (adjusted OR 31.86 per 100 kUA/L increase; 95% CI 1.60–636.15) remained independent predictors of OFC positivity. Conclusions: Absolute egg white SPT wheal diameter and serum sIgE independently predict OFC outcomes in egg-sensitized children. Histamine-normalized indices did not provide added value over wheal size alone. These findings support a probabilistic, context-based use of test results to inform selective OFC planning rather than replace OFC.