Determining specific IgE cutoff values to predict reactions in oral food challenges for cow's milk allergy using the Immulite System.

The diagnosis of IgE-mediated cow's milk allergy (CMA) involves serum-specific IgE (spIgE), skin prick tests (SPT), and the gold standard oral food challenge (OFC). SpIgE levels are measured using methods such as ImmunoCAP and IMMULITE, with most cutoff data derived from ImmunoCAP. This study aims to determine IMMULITE-specific cutoff values to predict OFC positivity. Patients diagnosed with CMA via OFC between 2019 and 2023 were retrospectively analyzed. Data on demographics, eosinophil counts, total and specific IgE levels, and SPT results were collected. OFC was conducted using yogurt, milk-based formula, or milk-containing muffins. SPTs were performed with commercial extracts (Lofarma®) and pasteurized milk using the prick-to-prick method. SpIgE levels were measured with the Siemens® IMMULITE 2000 Immunoassay System, with values ≥0.35 kU/L considered positive. The study included 50 OFC-positive patients (60% males) and 50 age- and clinically matched controls without objective OFC reactions. The median age at diagnosis was 6 months (IQR: 3-21), and 52% presented with atopic dermatitis. OFC reactions occurred with yogurt in 42 patients (84%), muffins in 6, and milk in 2; 26% of reactions were anaphylaxis. IMMULITE-derived cutoff values were 3.13 kU/L (AUC: 0.776, 72% sensitivity, 72% specificity) for cow's milk spIgE and 1.85 kU/L for casein. SPT enduration cutoffs were 4.25 mm for pasteurized milk and 3.5 mm for commercial extracts. This study provides critical IMMULITE-specific spIgE cutoffs to predict OFC outcomes, offering valuable reference ranges for clinical CMA diagnosis.