Short-term mortality risk of serum potassium levels in hypertension: a retrospective analysis of nationwide registry data

Aims : Diuretics and renin-angiotensin-aldosterone system inhibitors are central in the treatment of hypertension, but may cause serum potassium abnormalities. We examined mortality in relation to serum potassium in hypertensive patients. Methods and results : From Danish National Registries, we identified 44 799 hypertensive patients, aged 30 years or older, who had a serum potassium measurement within 90 days from diagnosis between 1995 and 2012. All-cause mortality was analysed according to seven predefined potassium levels: < 3.5 (hypokalaemia), 3.5-3.7, 3.8-4.0, 4.1-4.4, 4.5-4.7, 4.8-5.0, and.5.0 mmol/L (hyperkalaemia). Outcome was 90-day mortality, estimated with multivariable Cox proportional hazard model, with the potassium interval of 4.1-4.4 mmol/L as reference. During 90-day follow-up, mortalities in the seven strata were 4.5, 2.7, 1.8, 1.5, 1.7, 2.7, and 3.6%, respectively. Adjusted risk for death was statistically significant for patients with hypokalaemia [hazard ratio (HR): 2.80, 95% confidence interval ( 95% CI): 2.17-3.62], and hyperkalaemia (HR: 1.70, 95% CI: 1.36-2.13). Notably, normal potassium levels were also associated with increased mortality: K: 3.53.7 mmol/L (HR: 1.70, 95% CI: 1.36-2.13), K: 3.8-4.0 mmol/L (HR: 1.21, 95% CI: 1.00-1.47), and K: 4.8-5.0 mmol/L (HR: 1.48, 95% CI: 1.15-1.92). Thus, mortality in relation to the seven potassium ranges was U-shaped, with the lowest mortality in the interval of 4.1-4.4 mmol/L. Conclusion : Potassium levels outside the interval of 4.1-4.7 mmol/L were associated with increased mortality risk in patients with hypertension.