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Hyponatremia and mortality risk: a Danish cohort study of 279 508 acutely hospitalized patients

2015; Oxford University Press; Volume: 173; Issue: 1 Linguagem: Inglês

10.1530/eje-15-0111

1479-683X

Louise Holland-Bill, Christian Fynbo Christiansen, Uffe Heide‐Jørgensen, Sinna Pilgaard Ulrichsen, Troels Ring, Jens Otto Lunde Jørgensen, Henrik Toft Sørensen,

Ion Transport and Channel Regulation

Objective We aimed to investigate the impact of hyponatremia severity on mortality risk and assess any evidence of a dose–response relation, utilizing prospectively collected data from population-based registries. Design Cohort study of 279 508 first-time acute admissions to Departments of Internal Medicine in the North and Central Denmark Regions from 2006 to 2011. Methods We used the Kaplan–Meier method (1 – survival function) to compute 30-day and 1-year mortality in patients with normonatremia and categories of increasing hyponatremia severity. Relative risks (RRs) with 95% CIs, adjusted for age, gender and previous morbidities, and stratified by clinical subgroups were estimated by the pseudo-value approach. The probability of death was estimated treating serum sodium as a continuous variable. Results The prevalence of admission hyponatremia was 15% (41 803 patients). Thirty-day mortality was 3.6% in normonatremic patients compared to 7.3, 10.0, 10.4 and 9.6% in patients with serum sodium levels of 130–134.9, 125–129.9, 120–124.9 and <120 mmol/l, resulting in adjusted RRs of 1.4 (95% CI: 1.3–1.4), 1.7 (95% CI: 1.6–1.8), 1.7 (95% CI: 1.4–1.9) and 1.3 (95% CI: 1.1–1.5) respectively. Mortality risk was increased across virtually all clinical subgroups, and remained increased by 30–40% 1 year after admission. The probability of death increased when serum sodium decreased from 139 to 132 mmol/l. No clear increase in mortality was observed for lower concentrations. Conclusions Hyponatremia is highly prevalent among patients admitted to Departments of Internal Medicine and is associated with increased 30-day and 1-year mortality risk, regardless of underlying disease. This risk seems independent of hyponatremia severity.