Evaluation of sIgE Qualitative Conversion and Clinical Response to HDMs Sublingual Immunotherapy: Insights from Three Immunoassays

Background: Sublingual immunotherapy (SLIT) is an effective treatment for house dust mite (HDM)-induced allergic rhinitis (AR); however, the significance of qualitative changes in specific IgE (sIgE) remains unclear. This study evaluated post-treatment changes in sIgE reactivity and compared the performance of three immunoassays. Methods: In this prospective study, monosensitized patients with HDM-induced AR were identified using skin prick testing and followed for 12 months after SLIT. Serum sIgE levels were assessed at baseline and after treatment using immunoblot, chemiluminescent immunoassay (CLIA), and ImmunoCAP as the reference method. Qualitative changes in sIgE reactivity were analyzed. Clinical response was assessed using the total nasal symptom score (TNSS), and total IgE (tIgE) levels were measured. Results: At baseline, HDM-sIgE reactivity was detected in 85.7%, 82.1%, and 92.9% of patients by immunoblot, CLIA, and ImmunoCAP, respectively. Following SLIT, a significant qualitative conversion to non-reactive status was observed across all assays (p < 0.001). Conversion rates were 94.0% for immunoblot, 83.3% for CLIA, and 100.0% for ImmunoCAP. Significant improvements in TNSS and reductions in tIgE were also observed. Conclusions: SLIT induces a marked qualitative reduction in HDM-sIgE reactivity, with complete serological conversion detected by ImmunoCAP. Although the immunoassays showed comparable rates of HDM-sIgE detection, their agreement in classifying individual patients differed, indicating variability in assay performance. Qualitative assessment of sIgE may provide a clinically meaningful approach for monitoring immunotherapy response.