Studies on the relationship between the level of specific IgE antibodies and the clinical expression of allergy: I. Definition of levels distinguishing patients with symptomatic from patients with asymptomatic allergy to common aeroallergens

Background: The detection of specific IgE antibodies to environmental allergens does not always coincide with a diagnosis of clinically evident allergic disease, because some patients with positive skin and/or in vitro test results have no symptoms related to the allergen or allergens that induced the antibodies. Objective: In a multicenter study the optimal cutoff values for specific IgE antibody levels and skin test results that could discriminate between patients with symptomatic and those with asymptomatic allergy were determined. Methods: IgE antibodies specific for a panel of common aeroallergens were assayed with the Pharmacia CAP system (Pharmacia, Uppsala, Sweden) in two groups of patients, a group of 267 patients with symptomatic allergy and a group of 243 healthy, nonallergic control subjects. The cutoff values were established by receiver operating characteristic analysis. Results: A significantly higher mean specific IgE antibody value was found in patients with symptomatic allergy compared with patients with asymptomatic allergy (p < 0.001) and in patients with symptomatic allergy compared with healthy control subjects (p < 0.001). The optimal cap system cutoff value between patients with symptomatic and those with asymptomatic allergy was 11.7 kU/L and when seasonal allergens were compared with perennial allergens, the cutoffs were 10.8 kU/L and 8.4 kU/L, respectively. The optimal cutoff value for the skin prick test was a wheal area 32 mm(2) for seasonal allergens and 31 mm(2) for perennial allergens. The skin test had a lower diagnostic value (sum of sensitivity and specificity) than the CAP system Conclusions: Cutoff values for specific serum IgE antibody levels are likely to be useful in clinical practice to distinguish symptomatic from asympotomatic allergy in patients with positive skin test results.