Elevated baseline potassium level within reference range is associated with worse clinical outcomes in hospitalised patients.

The clinical significance of elevated baseline serum potassium (K) levels in hospitalised patients is rarely described. Hence, we performed a retrospective study assessing the significance of elevated K levels in a one-year admission cohort. Adult patients without hypokalaemia or end-stage renal disease were included. Adverse outcomes were all-cause mortality, hospital-acquired acute kidney injury, and events of arrhythmia. In total, 17,777 patients were included in the study cohort, and a significant difference (P < 0.001) was observed in mortality according to baseline serum K levels. The adjusted hazard ratios (HRs) and associated 95% confidence intervals (CIs) of all-cause mortality for K levels above the reference range of 3.6-4.0 mmol/L were as follows: 4.1-4.5 mmol/L, adjusted HR 1.075 (95% CI 0.981-1.180); 4.6-5.0 mmol/L, adjusted HR 1.261 (1.105-1.439); 5.1-5.5 mmol/L, adjusted HR 1.310 (1.009-1.700); >5.5 mmol/L, adjusted HR 2.119 (1.532-2.930). Moreover, the risks of in-hospital acute kidney injury and arrhythmia were higher in patients with serum K levels above 4.0 mmol/L and 5.5 mmol/L, respectively. In conclusion, increased serum K levels, including mild elevations may be related to worse prognosis. Close monitoring and prompt correction of underlying causes or hyperkalaemia itself is warranted for admitted patients.