Urine anti-PLA2R antibody is a novel biomarker of idiopathic membranous nephropathy

Since urine samples more directly reflect kidney alterations and damage than blood samples, we investigated whether urine anti-PLA2R antibody (uPLA2R-Ab) could be utilized similarly to serum anti-PLA2R antibody (sPLA2R-Ab) as a noninvasive biomarker of idiopathic membranous nephropathy (IMN). In this study, we performed a qualitative analysis using an indirect immunofluorescence test (IIFT) and measured uPLA2R-Ab and sPLA2R-Ab concentrations using an enzyme-linked immunosorbent assay (ELISA) in 28 patients with biopsy-proven IMN and 12 patients with secondary membranous nephropathy (SMN). Overall, 64.3% (n=18) of patients with IMN had IIFT-positive sPLA2R-Ab, 67.9% (n=19) of patients with IMN had IIFT-positive uPLA2R-Ab, and none of the SMN patients had IIFT-positive sPLA2R-Ab or uPLA2R-Ab. The titers of the anti-PLA2R antibody from the IMN patients in the urine (10.72±22.24 RU/μmol, presented as uPLA2R-Ab/urine creatinine) and serum (107.36±140.93 RU/ml) were higher than those from the SMN patients (0.51±0.46 RU/μmol, 0.008±0.029 RU/ml, respectively, p<0.05). Statistical analyses indicated that there were positive correlations between uPLA2R-Ab and gPLA2R, sPLA2R-Ab or urinary protein and negative correlations between uPLA2R-Ab and serum albumin in patients with IMN. In conclusion, uPLA2R-Ab is a novel biomarker of IMN. sPLA2R-Ab combined with uPLA2R-Ab might be more helpful for diagnosis and activity in PLA2R associated MN.