Methods: In this nationwide cross-sectional study, 3,753 elementary schoolchildren (6-7 yr olds) and 3,930 middle schoolchildren (12-13 yr olds) were enrolled. Total IgE levels were measured and skin prick tests were performed for 18 common inhalant allergens. Children and parents answered the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire. We analyzed the diagnostic value of total IgE by using ROC (Receiver operating characteristic) curve and compared total IgE levels according to atopy and allergic diseases such as atopic dermatitis, bronchial asthma and allergic rhinitis.
Results: The total IgE ranged from 1.5 to 4,523.1 kU/L in elementary schoolchildren and 1.5 to 3,000 kU/L in middle schoolchildren. The median total IgE level was 86.7 kU/L (75th percentile, 292.6 kU/L; 90th percentile, 698.5 kU/L; 95th percentile, 1,200.7 kU/L) in elementary schoolchildren and 94.7 kU/L (75th percentile, 284.3 kU/L; 90th percentile, 625.1 kU/L; 95th percentile, 990.7 kU/L) in middle schoolchildren. The median total IgE level was significantly higher in atopic group defined as any positive SPT (elementary schoolchildren, 246.5 kU/L; P<0.0001, middle schoolchildren, 206.1 kU/L; P<0.0001) and any allergic disease group (elementary schoolchildren, 108.3 kU/L; P<0.0001, middle schoolchildren, 141.2 kU/L; P<0.0001). In ROC analysis of total IgE for diagnosing atopy, AUC was 0.7835 (95% CI, 0.7688-0.7982) in elementary schoolchildren and 0.8165 (95% CI, 0.8032-0.8297) in middle schoolchildren. At the optimal cut-off value of 127.7 kU/L in elementary schoolchildren and 63.0 kU/L in middle schoolchildren, sensitivity, specificity, and positive and negative predictive values were 67.06%, 75.38%, 65.44%, and 76.70% in elementary schoolchildren and 81.91%, 66.63%, 75.01% and 75.08% in middle schoolchildren respectively.
Conclusions: Total serum IgE level was higher in children with atopy or allergic diseases, but the value of total serum IgE as a diagnostic test for atopy is limited due to the low sensitivity and specificity.