Casein sIgE avidity and milk basophil reactivity in children with cow's milk allergy.

BACKGROUND: In our previous study, casein specific IgE (sIgE) was identified as the best predictor for heated milk (HM) tolerance. However, reaction severity and cumulative eliciting dose in oral food challenges (OFC) remain difficult to predict. The use of milk basophil activation test (BAT) and sIgE avidity has not been previously studied for this purpose in HM allergy without the presence of wheat matrix. Consequently, we aimed to investigate whether they could improve prediction of fresh milk (FM) and HM OFC outcomes, reaction severity, and cumulative eliciting dose. METHODS: 1-18-year-old Finnish children with suspected IgE-mediated cow's milk allergy underwent OFCs with both FM (N = 160) and HM (N = 138). sIgE to milk and its allergens was measured. Milk BAT using whole blood and casein sIgE avidity measurements using a thiocyanate-based ELISA assay were performed. RESULTS: Milk BAT showed better performance in discriminating allergy and tolerance in FM OFCs (N = 57, area under the curve (AUC) 0.946) than in HM OFCs (N = 42, AUC 0.686). Casein sIgE avidity did not differ between HM allergic and tolerant children (N = 56). Neither assay was associated with reaction severity or cumulative eliciting dose in FM or HM OFCs. CONCLUSION: Milk BAT performed well in FM allergy prediction, while in HM OFCs its diagnostic accuracy was modest and did not exceed that of casein sIgE. Casein sIgE avidity did not improve prediction of FM or HM OFC outcome, reaction severity, or cumulative dose. The avidity assay was also inherently limited by the requirement for casein sIgE levels of >1kU/L.