Postdialysis Hypokalemia and All-Cause Mortality in Patients Undergoing Maintenance Hemodialysis

Background and objectives Almost half of patients on dialysis demonstrate a postdialysis serum potassium <= 3.5 mEq/L. We aimed to examine the relationship between postdialysis potassium levels and all-cause mortality. Design, setting, patients, & measurements We conducted a cohort study of 3967 participants on maintenance hemodialysis from the Dialysis Outcomes and Practice Patterns Study in Japan (2009-2012 and 2012-2015). Postdialysis serumpotassiumwasmeasured repeatedly at 4-month intervals and used as a time-varying variable. We estimated the hazard ratio of all-cause mortality rate using Cox hazard regression models, with and without adjusting for time-varying predialysis serum potassium. Models were adjusted for baseline characteristics and time-varying laboratory parameters. We also analyzed associations of combinations of pre-and postdialysis potassium with mortality. Results The age of participants at baseline was 65 +/- 12 years (mean +/- SD), 2552 (64%) were men, and 96% were treatedwith a dialysate potassiumlevel of 2.0 to, 2.5mEq/L. Themedian follow-up periodwas 2.6 (interquartile range, 1.3-2.8) years. During the follow-up period, 562 (14%) of 3967 participants died, and the overallmortality ratewas 6.7 per 100 person-years. Compared with postdialysis potassiumof 3.0 to, 3.5mEq/L, the hazard ratios of postdialysis hypokalemia (, 3.0 mEq/L) were 1.84 (95% confidence interval, 1.44 to 2.34) in the unadjusted model, 1.44 (95% confidence interval, 1.14 to 1.82) in themodelwithout adjusting forpredialysis serumpotassium, and 1.10 (95% confidence interval, 0.84 to 1.44) in the model adjusted for predialysis serum potassium. The combination of pre-and postdialysis hypokalemia was associated with the highest mortality risk (hazard ratio, 1.72; 95% confidence interval, 1.35 to 2.19, reference; pre-and postdialysis nonhypokalemia). Conclusions Postdialysis hypokalemiawas associated withmortality, but this associationwas not independent of predialysis potassium.