Time-resolved fluoroimmunoassay improves sensitivity in the diagnosis of primary membranous nephropathy with low phospholipase A2 receptor antibody titer

To evaluate the diagnostic utility of time-resolved fluoroimmunoassay (TRFIA) for detecting serum anti-Phospholipase A2 Receptor (PLA2R) antibodies, specifically the IgG (PLA2R-IgG) and IgG4 subclass (PLA2R-IgG4). A total of 175 patients with serum anti-PLA2R antibody range from 2 to 20 RU/ml, between January 2018 and December 2024, were retrospectively analyzed. 121 serum specimen were tested by TRFIA and ELISA. According to renal biopsy, 52% (91/175) patients were diagnosed with primary membranous nephropathy (PMN). Notably, TRFIA exhibited higher sensitivity and specificity in identifying patients with PMN. Based on the manufacturer's recommended cutoff values, TRFIA demonstrated a higher sensitivity of 14.3% for PLA2R-IgG and 34.1% for PLA2R-IgG4 compared to ELISA (0%). Receiver operating characteristic analysis showed that TRFIA achieved an area under the curve (AUC) of 0.829 for PLA2R-IgG and 0.814 for PLA2R-IgG4.The optimal anti-PLA2R antibody cutoff values for diagnosing PMN were 0.44 RU/ml (PLA2R-IgG-TRFIA) and 25.07 ng/ml (PLA2R-IgG4-TRFIA) with a sensitivity/specificity of 83.3%/82.4% for PLA2R-IgG-TRFIA, and 83.3% /76.9% for PLA2R-IgG4-TRFIA, both of which were higher than those of ELISA (cutoff:2.84 RU/ml; sensitivity/specificity: 50%/88%). In conclusion, TRFIA demonstrates enhanced sensitivity and specificity in detecting anti-PLA2R antibodies, which may facilitate more accurate diagnosis of PMN and minimize the need for invasive renal biopsies.