Utility of diagnostic tests in the follow-up of egg-allergic children


Ma Carmen Diéguez Pastor, MD, PhD, Servicio de Alergología, Hospital Universitario Ramón y Cajal, Carretera de Colmenar Km 9.100, CP: 28034 Madrid, Spain. E-mails: maicadieguez@gmail.com; mcarmen.dieguez@salud.madrid.org


Background Better knowledge of the accuracy of a skin prick test (SPT) and specific IgE (sIgE) levels to egg allergens would help to identify persistent egg-allergic children, avoiding unnecessary risky challenges. This study was designed to assess the accuracy of a SPT and sIgE levels to egg allergens in order to determine persistent egg allergy in IgE-mediated allergic children after an egg-free diet.

Methods Children below 16 years were prospectively and consecutively recruited. Inclusion criteria were: allergy to egg proteins (children with a positive clinical case of IgE-mediated egg allergy and a positive SPT to egg allergens and/or positive sIgE levels), and strict egg avoidance diet followed for at least 6 months. Clinical histories were recorded and all patients underwent SPTs, sIgE levels to egg allergens and the gold standard -a double-blind placebo-controlled egg challenge (DBPCFG). DBPCFG was interpreted without knowledge of the results of the other tests and vice-versa. A SPT and sIgE levels' ROC curves analysis was performed to compare the diagnostic performance of the different tests.

Results Finally, 157 children were included in the study. One hundred out of these 157 children (63.7%) had a positive oral challenge. Ninety-six were male (61%), and the median age was 2.5 years. One hundred and three (66.9%) had atopic dermatitis. A 7 mm egg white prick test had a positive likelihood ratio (+LR) of 6.7, and a level of 1.3 KU/L egg white-sIgE had a +LR of 5.1. A 7 mm egg white SPT had a positive predictive value of 92.3% (95% CI 85.1–99.5), and for a 9 mm egg white SPT this value was 95.6% (95% CI 87.3–100.0). For egg white-sIgE, 1.5 KU/L had a positive predictive value of 90.4% (95% CI 82.4–98.4) and for 25 KU/L it was 100.0% (95% CI 100.0–100.0). SPTs with ovotransferrin and lysozyme showed the lowest accuracy, followed by yolk and ovalbumin SPTs.

Conclusion This study is the first to evaluate both tests (SPT and sIgE levels) and all egg allergens to determine the persistence of egg allergy in IgE-mediated allergic children. Measuring the SPT and sIgE levels is useful to predict persistent allergy in these children, especially with the egg white complete extract. An oral challenge should not be performed in egg allergic paediatric patients with either an egg white prick test above 7 mm or a white egg-sIgE determination above 1.3 KU/L, because there is a 90% probability of remaining allergic.