Objective To explore the role of phospholipase A2 receptor 1 (PLA2R1) in the diagnosis,differential diagnosis and evaluation of idiopathic membranous nephropathy (IMN) in adult patients.Methods A total of 242 renal disease patients diagnosed by renal biopsy from March 2015 to January 2016 were enrolled,consisting of 90 IMN,20 secondary membranous nephropathy (SMN),82 IgA nephropathy (IgAN),30 minimal changed disease (MCD),16 focal segmental glomerulosclerosis (FSGS) and 4 membranoproliferative glomerulonephritis (MPGN).Their clinical data including age,sex,serum creatinine (Scr),serum albumin and 24 h urinary protein were collected.Serum PLA2R1 was measured by enzyme linked immunosorbent assay.PLA2R and IgG subclasses in glomeruli were detected by indirect immunofluorescence assay.The positive rate of serum PLA2R1 among those groups and its correlation with clinical-pathological parameters were analyzed.Results Compared with IMN patients,SMN,MCD and FSGS patients were younger (all P ＜ 0.01); IgAN patients were younger and had higher serum albumin and lower 24 h proteinuria (all P ＜ 0.001); MPGN patients had higher Scr (all P ＜ 0.01).The positive rate of serum PLA2R1 was 75.6％ in IMN patients,while it was 0.0％ in non-IMN patients.The distribution between serum PLA2R1 and pathological diagnosis had difference (P ＜ 0.001),their positive coincidence rate was 100％,negative coincidence rate was 87.4％,total coincidence rate was 90.9％ and their consistency was well (Kappa=0.795,P ＜ 0.001).Among IgG subtype comparisons between IMN patients and SMN patients in the glomeruli,only moderate or more positive IgG4 had statistical differences (82.2％ vs 5.0％,P ＜ 0.001); the positive rate of glomerular PLA2R1 was 41.1％ in IMN patients,higher than 10.0％ in SMN patients (P=0.009); positive PLA2R1 with moderate or more positive IgG4 in glomeruli in IMN patients was more than that in SMN patients (40.0％ vs 0.0％,P ＜ 0.001),which could improve the diagnostic specificity of IMN.In IMN patients serum PLA2R1 and glomerular PLA2R1 had statistical differences (P＜0.001).Spearman rank correlation analysis showed that serum PLA2R1 of IMN patients positively correlated with 24 h proteinuria (r=0.315,P=0.002),negatively correlated with serum albumin (r=-0.228,P=0.030) and didn't correlate with Scr (r=0.199,P=0.059).Conclusions Serum PLA2R can be used as the specific indicator for diagnosis,differential diagnosis of IMN and to reflect the severity of IMN in patients.