Supplementary Material for: Clinical Characteristics and Outcomes of Hyperphosphatemia in patients with CKD Stages 1 to 2

Introduction: There was limited research on the epidemiology of hyperphosphatemia in early-stage chronic kidney disease (CKD) patients. We aimed to explore the clinical characteristics and prognostic value of hyperphosphatemia in patients with CKD stages 1-2.
Methods: We enrolled adult patients with CKD stages 1-2 from 24 regional central hospitals across China. Hyperphosphatemia was defined as a serum phosphate level exceeding 1.45 mmol/L. The study outcomes included all-cause and cardiovascular (CV) mortality. Cox proportional hazard models were used to investigate the association of hyperphosphatemia with all-cause and CV mortality.
Results: Among 99,266 patients with CKD stages 1-2 across China, the prevalence of hyperphosphatemia was 8.3%. The prevalence of hyperphosphatemia was increased with the level of urinary protein and was higher in younger and female patients. Among 63,121 patients with survival information, during a median of 5.2 years follow-up period, there were 436 (8.0%) and 4,695 (8.1%) deaths in those with and without hyperphosphatemia, respectively. After adjusting for potential confounders, compared with patients without hyperphosphatemia, patients with hyperphosphatemia was associated with a higher risk of all-cause mortality (HR, 1.28, 95% CI, 1.16-1.41). Although nearly 60.3% of hyperphosphatemia could be relieved without phosphate-lowering drug therapy among patients with CKD stages 1-2, transient hyperphosphatemia was also associated with an increased risk of all-cause mortality (P=0.048).
Conclusions: Hyperphosphatemia was not rare in patients with CKD stages 1-2 and was associated with an increased risk of mortality. Clinicians should closely monitor serum phosphorus levels in patients with CKD, even in those with normal kidney function.

研究背景：目前针对早期慢性肾脏病（chronic kidney disease, CKD）患者高磷血症的流行病学研究较为匮乏。本研究旨在探讨CKD 1-2期患者高磷血症的临床特征及其预后价值。
研究方法：本研究从全国24家区域中心医院纳入CKD 1-2期成年患者。高磷血症定义为血清磷酸盐水平超过1.45 mmol/L。本研究的结局指标包括全因死亡与心血管（cardiovascular, CV）死亡。采用Cox比例风险模型分析高磷血症与全因死亡、心血管死亡的关联。
研究结果：全国范围内纳入的99266例CKD 1-2期患者中，高磷血症患病率为8.3%。高磷血症患病率随尿蛋白水平升高而升高，且在年轻患者及女性患者中更高。在63121例拥有生存信息的患者中，中位随访5.2年期间，高磷血症组与非高磷血症组分别有436例（8.0%）与4695例（8.1%）患者死亡。校正潜在混杂因素后，与非高磷血症患者相比，高磷血症患者全因死亡风险升高（风险比HR=1.28，95%置信区间CI：1.16~1.41）。尽管CKD 1-2期患者中近60.3%的高磷血症无需降磷药物治疗即可缓解，但一过性高磷血症仍与全因死亡风险升高相关（P=0.048）。
研究结论：CKD 1-2期患者中高磷血症并非少见，且与死亡风险升高相关。临床医师应密切监测CKD患者的血清磷水平，即便肾功能正常者亦不例外。