Supplementary Material for: Serum phosphorus might be a predictor of kidney disease progression in IgA nephropathy

Introduction High serum phosphorus level has been reported to be a risk factor for disease progression in patients with chronic kidney disease. Whereas, its role in IgA nephropathy (IgAN) still remains uncertain. This study aimed to investigate the association between serum phosphorus and progression of IgAN. Methods A total of 247 patients diagnosed with IgAN from 2016.11 to 2019.12 at the First Affiliated Hospital of Xian Jiaotong University were retrospectively enrolled in this study. The association between serum phosphorus with kidney disease progression events, defined as 30% estimated glomerular filtration rate (eGFR) decline and kidney failure, was evaluated using Cox models. Results Serum phosphorus was an independent risk factor for poor renal outcome after adjusting for age, gender, urine protein, MAP, eGFR, hemoglobin, Oxford S and T scores (HR, 2.586; 95% CI, 1.238-5.400, P = 0.011). The addition of serum phosphorus to the reference model containing clinical and pathological variables significantly improved the risk prediction of IgAN progression (C statistic, 0.836; 95% CI, 0.783-0.889) as compared with the reference model (C statistic, 0.821; 95% CI, 0.756-0.886). The ability of serum phosphorus level to predict progression was much stronger in IgAN patients without use of immunosuppression (HR 5.173; 95%CI, 1.791-14.944); P=0.002). Conclusion Higher serum phosphorus levels were independently associated with kidney disease progression in patients with IgAN, especially in those without immunosuppression. The addition of serum phosphorus to clinical and pathological data at the time of biopsy significantly improved risk prediction of IgAN progression.引言：已有研究表明，高血清磷水平是慢性肾脏病（chronic kidney disease, CKD）患者疾病进展的危险因素。然而，其在IgA肾病（IgA nephropathy, IgAN）中的作用仍不明确。本研究旨在探讨血清磷水平与IgA肾病进展之间的关联。 方法：本研究回顾性纳入了2016年11月至2019年12月期间，西安交通大学第一附属医院确诊的247例IgA肾病患者。以估算肾小球滤过率（estimated glomerular filtration rate, eGFR）下降30%及肾衰竭作为肾脏疾病进展事件，采用Cox模型评估血清磷水平与该进展事件之间的关联。 结果：在校正年龄、性别、尿蛋白、平均动脉压（mean arterial pressure, MAP）、估算肾小球滤过率、血红蛋白、牛津分型S及T评分后，血清磷水平仍是肾脏不良预后的独立危险因素（风险比（hazard ratio, HR）=2.586；95%置信区间（confidence interval, CI）=1.238~5.400，P=0.011）。将血清磷水平加入包含临床及病理变量的基准模型后，相较于基准模型（C统计量=0.821；95%CI=0.756~0.886），该模型对IgA肾病进展的风险预测能力显著提升（C统计量=0.836；95%CI=0.783~0.889）。在未使用免疫抑制治疗的IgA肾病患者中，血清磷水平预测疾病进展的能力更强（HR=5.173；95%CI=1.791~14.944；P=0.002）。 结论：IgA肾病患者的血清磷水平升高与肾脏疾病进展独立相关，尤其是在未接受免疫抑制治疗的患者中。将血清磷水平加入活检时获取的临床及病理数据中，可显著提升IgA肾病进展的风险预测效能。