Diagnostic utility of allergy tests to predict baked egg and lightly cooked egg allergies compared to double-blind placebo-controlled food challenges

Abstract

Background: Double-blind placebo-controlled food challenges (DBPCFC) are the gold-standard to diagnose food allergy. However, they can cause allergic reactions of unpredictable severity. We assessed accuracy of current and new diagnostic tests compared to DBPCFC to baked egg (BE) and to lightly cooked egg (LCE). Methods: Children aged 6 months to 15 years were assessed for possible egg allergy as part of the BAT2 study (NCT03309488). They underwent clinical assessment, skin prick test (SPT), specific IgE (sIgE) and basophil activation test (BAT). The results of the tests were compared with DBPCFC outcomes to both BE and LCE. Results: A total of 150 children underwent DBPCFC to BE, 60 (40%) reacted to and 85 (57%) tolerated BE and 5 (3%) had inconclusive oral food challenges (OFC). Seventy-seven children tolerant to BE had DBPCFC to LCE and 16 reacted. The test within each modality with the best diagnostic performance for BE allergy was as follows: SPT to egg white (EW) (AUC = 0.726), sIgE to EW (AUC = 0.776) and BAT to egg (AUC = 0.783). BAT (AUC = 0.867) was the best test in the younger than 2 years age group. Applying 100% sensitivity and 100% specificity cut-offs, followed by OFC, resulted in 100% diagnostic accuracy. BAT enabled the greatest reduction in OFC (41%). Using sIgE followed by BAT allowed to reduce the number of BATs performed by about 30% without significantly increasing the number of OFC. Conclusions: The best diagnostic test was BAT to egg in terms of diagnostic accuracy and reduction in number of OFC. Using sIgE to EW followed by BAT required fewer BATs with sustained OFC reduction and diagnostic accuracy.