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 and its fractions with results of the oral challenge test, and to establish cutoff points capable of predicting clinical reactivity to cow's milk 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 cow's milk and presence of specific IgE for cow's milk and/or its fractions (positive skin and/or IgE serum tests) were submitted to open oral challenge test with cow's milk.

Results: The oral challenge test was positive in 59.8% of the children, 49% of whom were males. Serum levels of specific IgE, as well as mean cow's milk 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 cow's milk and its fractions capable of predicting cow's milk reactivity (positive oral challenge test) were: 5.17kUA/L for cow's milk, 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 cow's milk 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 cow's milk were: 5.17kUA/L for serum-specific IgE and 3.5mm for papule diameter measurement, values considered discriminatory for the diagnosis of cow's milk allergy.