Supplementary Material for: Serum Potassium Levels and Mortality in Hemodialysis Patients: A Retrospective Cohort Study

Background: Hyperkalemia is common in patients receiving maintenance hemodialysis. However, few studies have examined the association between serum potassium level and mortality. Methods: This study used annual cohorts of hemodialysis patients during 2007-2010. To determine hyperkalemia prevalence, monthly hyperkalemia was defined as serum potassium level ≥5.5 mEq/l; prevalence was calculated as a ratio of hyperkalemia episodes to follow-up time, reported separately by long and short interdialytic interval. To determine the impact of hyperkalemia on mortality, patients in the 2010 cohort were followed from first potassium measurement until death or a censoring event; hyperkalemia was defined, sequentially, by potassium levels 5.5-6.0 mEq/l at 0.1 mEq/l intervals. Time-dependent Cox proportional hazards modeling was used to estimate the association between hyperkalemia and mortality. Results: The 4 annual cohorts ranged from 28,774 to 36,888 patients. Mean age was approximately 63 years, about 56% were men, 51% were white and 44% had end-stage renal disease caused by diabetes. Hyperkalemia prevalence was consistently estimated at 16.3-16.8 events per 100 patient-months. Prevalence on the day after the long interdialytic interval was 2.0-2.4 times as high as on the day after the short interval. Hyperkalemia, when defined as serum potassium ≥5.7 mEq/l, was associated with all-cause mortality (adjusted hazards ratio (AHR) 1.13, 95% CI 1.01-1.28, p = 0.037, vs. <5.7 mEq/l) after adjustment. AHRs increased progressively as the hyperkalemia threshold increased, reaching 1.37 (95% CI 1.16-1.62, p < 0.0001) for ≥6.0 mEq/l. Conclusions: The long interdialytic interval was associated with increased likelihood of hyperkalemia. Hyperkalemia was associated with all-cause mortality beginning at serum potassium ≥5.7 mEq/l; mortality risk estimates increased ordinally through ≥6.0 mEq/l, suggesting a threshold at which serum potassium becomes substantially more dangerous.

背景：高钾血症（Hyperkalemia）在维持性血液透析患者中较为常见，但目前鲜有研究探讨血清钾水平与死亡率之间的关联。
方法：本研究纳入2007-2010年的血液透析患者年度队列。为明确高钾血症的患病率，将血清钾≥5.5 mEq/L定义为月度高钾血症；患病率以高钾血症发作次数与随访时间的比值计算，并按长、短透析间期分别报告。为明确高钾血症对死亡率的影响，本研究对2010年队列中的患者从首次血钾检测开始随访，直至患者死亡或发生删失事件；高钾血症依次以0.1 mEq/L为步长，按5.5~6.0 mEq/L的血钾水平进行定义。本研究采用时依性Cox比例风险模型估算高钾血症与死亡率之间的关联。
结果：4个年度队列的患者数量介于28774至36888例之间。受试者平均年龄约为63岁，男性占比约56%，白人占比51%，44%的患者患有糖尿病相关性终末期肾病。高钾血症患病率稳定在16.3~16.8次/100患者-月。长透析间期次日的高钾血症患病率是短透析间期次日的2.0~2.4倍。当高钾血症定义为血清钾≥5.7 mEq/L时，校正后分析显示其与全因死亡率显著相关（校正后风险比（adjusted hazards ratio, AHR）为1.13，95%置信区间（CI）1.01~1.28，P=0.037，对照基线为血钾<5.7 mEq/L）。随着高钾血症阈值升高，校正后风险比呈渐进式升高，当阈值≥6.0 mEq/L时，AHR达到1.37（95%CI 1.16~1.62，P<0.0001）。
结论：长透析间期与高钾血症发生风险升高相关。当血清钾≥5.7 mEq/L时，高钾血症即与全因死亡率相关；随着血钾水平升高至≥6.0 mEq/L，死亡风险呈有序递增，提示存在一个使血清钾水平显著升高不良风险的临界阈值。