Thickened Perirenal Fat Predicts Poor Renal Outcome in Patients with IgA Nephropathy: A Population-Based Retrospective Cohort Study

Introduction: Perirenal fat is a pad that fills the retroperitoneal space outside the kidney, which affects kidney function in various ways. However, the association between perirenal fat and IgA nephropathy (IgAN) has not yet been elucidated. This study aimed to investigate the role of perirenal fat in predicting IgAN progression. Methods: A total of 473 patients with biopsy-proven IgAN were recruited, and perirenal fat thickness (PFT) was measured using color Doppler ultrasonography. Patients were divided into two groups according to the median PFT: low PFT group (PFT <= 1.34 cm, n=239) and high PFT group (PFT>1.35 cm, n=234). A total of 473 healthy participants were included in the control group. Basic clinical characteristics were assessed at the time of renal biopsy, and the relationship between PFT and combined endpoints was analyzed. The combined endpoints were defined as a two-fold increase in blood creatinine level, end-stage renal disease (ESRD), and dialysis over three months. KaplanMeier survival analysis was used to explore the role of PFT in the progression of IgAN. Three clinicopathological models of multivariate Cox regression analysis were established to evaluate the association between PFT and renal prognosis in patients with IgAN. Results: Compared to healthy subjects, patients with IgAN showed significantly higher PFT. After a median follow-up of 50 months, 75 of 473 patients (15.9%) with IgAN reached renal combined endpoints. Among these, 13 in 239 patients (5.4%) were in the low PFT group and 62 of 234 patients (26.5%) were in the high PFT group (p<0.001). The results of three Cox regression models (including demographics, pathological and clinical indicators, and PFT) demonstrated that a higher PFT was significantly associated with a higher risk of reaching combined endpoints in patients with IgAN. Conclusion: This study indicated a positive relationship between PFT and renal progression in patients with IgAN, suggesting that perirenal fat might act as a marker of poor prognosis in patients with IgAN.