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: 3.5–3.7 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: