Average hyperkalemia between 5.5 and 6.4 mEq/L does not increase mortality in patients undergoing dialysis

Abstract Background The impact of hyperkalemia on mortality in cohort studies is difficult to assess because of fluctuations in serum potassium (S-K) levels, differences in the intensity of intervention for S-K, and the reliability of S-K levels measured across multiple facilities. Because our corporation has intervened for hyperkalemia when centrally measured S-K levels are ≥ 6.5 mEq/L, we investigated whether average S-K levels of 5.5–6.4 mEq/L were associated with higher mortality. Methods This retrospective observational study included 678 patients undergoing dialysis who were divided into low (3.5–4.4 mEq/L), intermediate (4.5–5.4 mEq/L), and high (5.5–6.4 mEq/L) groups according to average S-K level, excluding those with levels ≥ 6.5 mEq/L at least once during the 3 months before the start of the study. The 2-year all-cause mortality was compared using a propensity score-matching (PSM) model with annually censoring of patients who had S-K levels of ≥ 6.5 mEq/L at least once after 10–12 months. Kaplan–Meier survival curves were compared using the log-rank test, after which Cox regression analysis was performed with adjustments. Results After PSM, S-K levels were 4.1 ± 0.2 mEq/L in the low group and 5.7 ± 0.2 in the high group ( P < 0.001). Mortality was not significantly different between the two groups. After PSM, S-K levels were 4.9 ± 0.3 mEq/L in the intermediate group and 5.7 ± 0.2 in the high group ( P < 0.001). Mortality was significantly lower in the high group compared with the intermediate group (hazard ratio 0.120, 95% confidence interval 0.015–0.956, P = 0.016, log-rank test). However, the adjusted Cox regression analysis showed no significant difference between the groups. Conclusions These results suggested that mortality is not higher in dialysis patients with average S-K levels of 5.5–6.4 mEq/L than in those with average 3.5–4.4 mEq/L or 4.5–5.4 mEq/L when the interventional S-K levels were standardized to ≥ 6.5 mEq/L, and patients with S-K levels of ≥ 6.5 mEq/L were excluded or censored. Trial registration: UMIN Clinical Trials Registry, UMIN000056789. Registered 22 January, 2025, Prospectively registered, https://center6.umin.ac.jp/cgi-bin/ctr/ctr_view_reg.cgi?recptno=R000064682 .