Relationship between serum sodium level at dialysis initiation and all-cause mortality

Background: Hyponatremia is a common electrolyte disorder in patients with chronic kidney disease. In addition, hyponatremia is associated with mortality in patients with chronic kidney disease, including those on dialysis. However, few studies have examined this relationship in patients with incident dialysis. Methods: We used a database of multicenter prospective cohort studies that included 1520 incident dialysis patients. The baseline was set at the time of dialysis initiation. The enrolled patients were classified into five groups according to their serum sodium levels (< 130 mEq/L, 130–134 mEq/L, 135–139 mEq/L, 140–144 mEq/L, and ≥ 145 mEq/L). Multivariate Cox proportional hazards analysis was conducted to determine factors associated with all-cause mortality. Results: A total of 392 all-cause deaths occurred during the follow-up period. The ultrafiltration volume per body weight during the first dialysis session was more significant in the groups with the lowest and highest sodium levels. The percentage of patients using loop diuretics and thiazide was higher in the group with lower sodium levels (< 130 mEq/L and 130–134 mEq/L). All-cause mortality was significantly different among the five groups (p = 0.025). Multivariate analysis indicated that all-cause mortality was significantly higher in the group with the lowest sodium level compared to the group with a serum sodium level of 135–139 mEq/L (hazard ratio: 1.61, 95% confidence interval: 1.04–2.49). Conclusion: Hyponatremia of < 130 mEq/L at dialysis initiation was significantly associated with all-cause mortality. We considered the results relevant to underlying conditions, including cardiovascular disease and medications.