Accuracy of serum IgE concentrations and papule diameter in the diagnosis of cow's milk allergy.

OBJECTIVE To compare serum concentrations of specific IgE and mean papule diameters induced in the immediate skin reactivity test with cow's milk (CM) and its fractions with results of the oral challenge test (OCT), and to establish cutoff points capable of predicting clinical reactivity to CM in patients treated at a referral service. METHODS One hundred and twenty-two children (median of 17 months) with a history of immediate reactions to CM and presence of specific IgE for CM and/or its fractions (positive skin and/or IgE serum tests) were submitted to open OCT with CM. RESULTS The OCT was positive in 59.8% of the children, 49% of whom were males. Serum levels of specific IgE, as well as mean CM papule diameters, were significantly higher in allergic patients (medians: 3.39kUA/L vs. 1.16kUA/L, 2.5mm vs. 0mm). The optimal cutoff points (Youden's index) of serum IgE specific for CM and its fractions capable of predicting CM reactivity (positive OCT) were: 5.17kUA/L for CM, 0.95kUA/L for α-lactalbumin, 0.82kUA/L for β-lactoglobulin, and 0.72kUA/L for casein, whereas for papule diameters the cutoff points were 3.5mm for CM and 6.5mm, 9.0mm, and 3.0mm for the α-lactalbumin, β-lactoglobulin, and casein fractions, respectively. CONCLUSIONS The cutoff points capable of predicting clinical reactivity to CM were: 5.17kUA/L for serum-specific IgE and 3.5mm for papule diameter measurement, values considered discriminatory for the diagnosis of CM allergy.