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(K+)homeostasis,and their dysfunction leads to electrolyte disorders.We aimed to examine the relationship between different levels of K+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 K+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 K+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 par-ticipants 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 K+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 K+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 K+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 K+has the potential to be a marker of disease severity among very elderly patients with AKI.