Supplementary Material for: 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.

引言：肾周脂肪是填充于肾外腹膜后间隙的脂肪垫，可通过多种途径影响肾脏功能。然而目前尚未阐明肾周脂肪与IgA肾病（IgA nephropathy, IgAN）之间的关联。本研究旨在探讨肾周脂肪在预测IgAN病情进展中的作用。

方法：共纳入473例经肾活检证实的IgAN患者，采用彩色多普勒超声测量肾周脂肪厚度（perirenal fat thickness, PFT）。根据PFT中位数将患者分为两组：低PFT组（PFT≤1.34 cm，n=239）与高PFT组（PFT>1.35 cm，n=234）；另纳入473名健康受试者作为对照组。于肾活检时评估患者的基础临床特征，并分析PFT与复合终点事件的相关性。复合终点事件定义为3个月内血肌酐水平升高至基线2倍、终末期肾病（end-stage renal disease, ESRD）或需接受透析治疗。采用Kaplan-Meier生存分析探讨PFT对IgAN病情进展的影响；构建3项临床病理多因素Cox回归模型，以评估IgAN患者的PFT与肾脏预后之间的关联。

结果：与健康受试者相比，IgAN患者的PFT显著升高。中位随访50个月后，473例IgAN患者中有75例（15.9%）达到肾脏复合终点事件。其中低PFT组239例患者中有13例（5.4%）达到终点，高PFT组234例患者中有62例（26.5%）达到终点（p<0.001）。3项Cox回归模型（纳入人口学资料、病理及临床指标与PFT）的分析结果显示，PFT升高与IgAN患者达到复合终点事件的风险升高显著相关。

结论：本研究证实IgAN患者的PFT与肾脏病情进展呈正相关，提示肾周脂肪可作为IgAN患者不良预后的预测标志物。