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

Abstract

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.

Figure 1

Flow diagram for the study population.

Figure 2

Kaplan-Meier survival curve of the study cohort according to baseline serum K⁺ levels.

Figure 3

Clinical characteristics related to all-cause mortality in the study cohort. The black boxes indicate the adjusted hazard ratios (HR) for each characteristic, and the horizontal lines indicates the 95% confidence intervals (CI). The hazard ratios are adjusted for the following variables; age, sex, history of cancer, ischaemic heart disease, heart failure, hypertension, diabetes mellitus, baseline estimated GFR and total CO₂, presence of hypoalbuminaemia (albumin level less than 3.5 g/dL), anaemia (haemoglobin level less than 11 g/dL), and baseline use of ACE I/ARBs, beta blockers, diuretics and NSAIDs. Baseline estimated GFR and total CO₂ were included in the analysis as continuous variables (natural unit), as the laboratory findings were directly related to levels of serum K⁺.

Figure 4

Penalized smoothing splines showing the relationship between baseline serum K⁺ levels and risks for each adverse outcome. The black, linear lines indicate the results of univariable analyses, and the black, broken lines indicate the results of multivariable analyses. The grey, dotted lines indicate the associated 95% confidence intervals. The multivariable analyses are adjusted for the following variables; age, sex, history of cancer, ischaemic heart disease, heart failure, hypertension, diabetes mellitus, baseline estimated GFR and total CO₂, presence of hypoalbuminaemia (albumin level less than 3.5 g/dL), anaemia (haemoglobin level less than 11 g/dL), and baseline use of ACE I/ARBs, beta blockers, diuretics and NSAIDs. Baseline estimated GFR and total CO₂ were included in the analysis as continuous variables (natural unit), as the laboratory findings were directly related to levels of serum K⁺.