Association of body composition-related indicators with urinary protein levels and proteinuria remission in patients with primary membranous nephropathy

Objective: To investigate the correlation between body composition-related indicators and urinary protein levels and proteinuria remission in patients with primary membranous nephropathy (PMN). Methods: This retrospective study enrolled patients with PMN who were diagnosed by renal biopsy, exhibiting a baseline urinary protein of ≥ 3.5g/d between July 2020 and May 2025. Body composition was assessed at enrollment using bioelectrical impedance analysis before any treatment. The predictors included percentage of body fat (PBF), fat mass index (FMI), and adipose tissue index (ATI). The relationship between body composition measures and proteinuria remission was studied by Kaplan–Meier analysis and Cox regression. Results: This study included 115 patients with PMN, of whom 75 (65.2%) were men, with a median age of 53.0 years. Significant differences in body composition–related indices, including PBF, FMI, and ATI, were observed between patients who achieved complete remission (CR) of proteinuria and those who did not (all P < 0.05). Univariate and multivariate Cox regression analyses demonstrated that PBF, FMI, and ATI were independently associated with proteinuria remission. Among these indices, FMI, which is unaffected by fluid overload, was independently and strongly associated with proteinuria remission (HR 0.858, 95% CI 0.757–0.972; P=0.016). Compared with non-obese patients, obese individuals (defined as FMI > 6 kg/m² in men and > 9 kg/m² in women) had higher baseline proteinuria levels. In sex-stratified analysis, non-obese men were 3.586 (95%CI: 1.387-9.27; P=0.008) times more likely to achieve CR than obese men. Conclusion: FMI was found to be positively correlated with proteinuria level in patients with PMN, and it emerged as an independent risk factor for complete remission of proteinuria.