Ultrasensitive Immunoassay Using a Novel Gd-IgA1 Antibody and Its Clinical Application in the Diagnosis of IgA Nephropathy

Introduction IgA nephropathy (IgAN) diagnosis remains dependent on invasive renal biopsy because currently available serologic biomarkers, including galactose-deficient IgA1 (Gd-IgA1), have limited diagnostic performance. This study aimed to develop and evaluate a high-sensitivity time-resolved fluorescence immunoassay (TRFIA) based on a novel anti-Gd-IgA1 monoclonal antibody (MH33) for Gd-IgA1 detection in IgAN. Methods MH33 glycoepitope specificity was characterized by surface plasmon resonance (SPR). A MH33-based TRFIA was developed and evaluated for analytical and diagnostic performance in healthy controls, non-IgAN renal disease controls, and IgAN patients, with comparison to a KM55-based assay. Results SPR analysis showed that MH33 recognized a GalNAc-modified IgA1 hinge-region glycopeptide distinct from the KM55 epitope. The MH33-based TRFIA achieved a detection limit of 0.20 Ru/mL, a quantification range of 0.20–600 Ru/mL, and acceptable analytical performance (intra-/inter-assay CVs: 2.32%–5.49% and 3.97%–5.23%; recoveries: 89.80%–103.76%). Correlation with KM55 was moderate (IgAN, r = 0.23, p =0.09). For distinguishing IgAN from combined controls (healthy controls and non-IgAN renal diseases), the MH33-based TRFIA yielded an AUC of 0.90 (95% CI: 0.86–0.93), compared with 0.78 (95% CI: 0.71–0.86) for KM55 . At the optimal cutoff value (22.0 Ru/mL), the assay achieved a specificity of 93.82% and sensitivity of 64.44%. Conclusion MH33-based TRFIA provides a sensitive approach for Gd-IgA1 detection and demonstrates favorable diagnostic performance for IgAN.