Association of serum potassium level with early and late mortality in very elderly patients with acute kidney injury.

Background: The kidneys play a central role in serum potassium ( ) homeostasis, and their dysfunction leads to electrolyte disorders. We aimed to examine the relationship between different levels of and mortality among very elderly patients with acute kidney injury (AKI).

Methods: We retrospectively enrolled very elderly patients (≥75 years) with AKI from the hospital information system of the Chinese PLA General Hospital from January 1, 2007 to December 31, 2018. All-cause mortality was examined according to six predefined levels: <3.50 mmol/L, 3.50-3.79 mmol/L, 3.80-4.09 mmol/L, 4.10-4.79 mmol/L, 4.80-5.49 mmol/L, and ≥5.50 mmol/L. We estimated the risk of all-cause mortality using the multivariable adjusted Cox proportional hazard model with the normal level at 3.50-3.79 mmol/L as a reference.

Results: In total, 747 patients were deemed suitable for the final evaluation. The median age of the 747 participants was 88 (84-91) years. After 90 days, the mortality rates in the six strata were 28.3%, 21.9%, 30.1%, 35.4%, 45.2%, and 58.3%, respectively. In the multivariable adjusted analysis, patients with levels of 4.10-4.79 mmol/L (hazard ratio [HR]: 1.638; 95% confidence interval [CI]: 1.016-2.642), 4.80-5.49 mmol/L (HR: 2.585; 95% CI: 1.524-4.384), and ≥5.50 mmol/L (HR: 2.587; 95% CI: 1.495-4.479) had an increased risk of all-cause mortality. After 1 year, the mortality rates in the six strata were 44.8%, 41.1%, 45.1%, 51.8%, 63.1%, and 76.3%, respectively. In the multivariable adjusted analysis, patients with levels of 4.10-4.79 mmol/L (HR: 1.452; 95% CI: 1.014-2.079), 4.80-5.49 mmol/L (HR: 2.151; 95% CI: 1.427-3.241), and ≥5.50 mmol/L (HR: 2.341; 95% CI: 1.514-3.620) had an increased risk of all-cause mortality.

Conclusion: Increased serum levels, including levels of 4.10-5.49 mmol/L and ≥5.50 mmol/L, were associated with a significantly increased short- and long-term risk of death. Serum has the potential to be a marker of disease severity among very elderly patients with AKI.