Sex-specific risks of death in patients hospitalized for hyponatremia: a population-based study

PURPOSE: Several studies have reported an association between hyponatremia and lethality. However, it remains elusive whether hyponatremia independently contributes to lethality. The aim of the study was to investigate associations between hyponatremia and lethality and differences in lethality between men and women hospitalized due to hyponatremia. METHODS: Four registries were utilized in this population-based retrospective study: The National Patient Registry, the Cause of Death Register, the Swedish Prescribed Drug Register and the Total Population Register (NPR) from which the controls were sampled. All hospitalized patients with a first-ever principal ICD10 diagnosis of hyponatremia or syndrome of inappropriate ADH secretion in the NPR between 1 October 2005 and 31 December 2014 were defined as cases. Cox regression with adjustment for potential confounders was used. RESULTS: 14,359 individuals with a principal diagnosis of hyponatremia, and 57,382 matched controls were identified. Median age was 76 years and the majority were women (72%). Median age for women and men was 79 and 68 years, respectively. Adjusted hazard ratios (and 95% CI) for lethality in those with hyponatremia compared with controls were for the entire population 5.5 (4.4–7.0) and in the subgroup free from previously known underlying disease 6.7 (3.3–13.3). Lethality in women with hyponatremia was lower compared with men: HR: 0.56 (0.49–0.64). In the healthier group the lethality remained lower for women: HR: 0.49 (0.34–0.71). CONCLUSIONS: Patients hospitalized due to hyponatremia faced an increased subsequent lethality that was independent of concomitant disease. This increase was nearly twice as large among men compared with women.