Serum Free IgE: a Useful Biomarker of Atopy and Type 2 Asthma in Adult Asthmatics.

BACKGROUND It has been known that a high serum total IgE level is a predisposing factor of allergic asthma; however, there are considerable limitations to apply it in clinical practice. OBJECTIVE The aim of this study is to determine the clinical significance of the serum free IgE level in patients with adult asthma. METHODS We measured free IgE levels using our home-made enzyme-linked immunosorbent assay (ELISA) via applying a novel IgE TRAP protein (GI innovation, Seoul, Korea) in sera of adult asthmatics (n = 116) compared to healthy controls (n = 32); ELISA inhibition test was performed to validate its binding specificity. Associations between asthma-related clinical and laboratory parameters were analyzed. The diagnostic value and cutoff point for detecting atopy and type 2 asthma were determined using receiver operating characteristic (ROC) curve analysis. RESULTS The serum free IgE levels were significantly higher in adult asthmatics than in healthy controls and were significantly associated with atopic status and type 2 asthma (all P < .001). In the ROC analysis, serum free IgE had a significantly greater area under the curve (AUC) than serum total IgE for assessing asthma, especially type 2 asthma (AUC = 0.810 vs 0.743, P = .006 and AUC = 0.729 vs 0.572, P < .001). The optimal cutoff points for predicting atopy and type 2 asthma were 82.8 and 120.8 ng/mL, respectively. CONCLUSION It is suggested that a higher serum free IgE level may be a useful biomarker of atopy and type 2 asthma in adult asthmatics.