Specific immunoglobulin E for aeroallergens: 0.35 kUA/L cutoff value is too low

Background: Measurement of specific immunoglobulin E (sIgE) is often used interchangeably with a skin-prick test (SPT) to detect allergic sensitization. Evidence of concordance between the two methods for aeroallergens in children is limited. Potentially, discordance can lead to misclassification in atopy diagnosis and subsequent clinical management. The arbitrary sIgE cutoff value of 0.35 kUA/L is used uniformly for all allergens. Objective: The aim of the study was to evaluate the agreement between sIgE with a cutoff of 0.35 kUA/L and a positive SPT result (cutoff of 3 mm) for 10 aeroallergens and to investigate the sIgE level that corresponds best with a positive SPT result in school-age children. Methods: Measurement of sIgE and SPT for birch, Timothy grass, mugwort, horse, dog, cat, Dermatophagoides pteronyssinus, Dermatophagoides farinae, Alternaria, and Cladosporium were performed in 300 children ages 6 to 14 years: 132 children with asthma and 168 controls. The agreement between sIgE and SPT results for the individual aeroallergens was assessed by using the Cohen κ coefficient with different sIgE cutoff values. Results: In total, the 300 children had 297 positive SPT results and 445 positive IgE analyses. The incidence of sensitization to Alternaria and Cladosporium was too low for further analysis. The agreement between the sIgE cutoff of 0.35 kUA/L and the SPT result cutoff of 3 mm was moderate to substantial for the remaining eight aeroallergens. The estimated optimal sIgE cutoff level that predicted an SPT result of ≥3 mm was 0.75 kUA/L for grass, horse, dog, and cat; 1.0 kUA/L for mugwort; 3.0 kUA/L for D. pteronyssinus; 5.0 kUA/L for birch; and 10.0 kUA/L for D. farinae. Using an sIgE cutoff of 0.75 kUA/L slightly increased the agreement for all eight allergens. Conclusion: Compared with an SPT result, a cutoff of 3 mm, analysis of our data suggests that an sIgE cutoff of 0.35 kUA/L is too low and that the optimal cutoff differs for the different aeroallergens.