Dysnatremia, Aging, and Vulnerability: Mortality and Discharge Outcomes in Hospitalized Adults

Background Dysnatremia, including hyponatremia and hypernatremia, is a common electrolyte abnormality among hospitalized patients and has been associated with adverse clinical outcomes. Older adults may be particularly vulnerable due to reduced physiological reserve and higher comorbidity burden; however, age-specific differences in the prognostic implications of dysnatremia and its association with post-acute care needs remain incompletely characterized. Methods We conducted a cross-sectional analysis of U.S. adult hospitalizations using a nationally representative inpatient database. Hospitalizations were classified by sodium status as normonatremia, hyponatremia, or hypernatremia and stratified by age (< 65 vs ≥ 65 years). Primary outcomes included in-hospital mortality and discharge disposition, with secondary outcomes including length of stay. Survey-weighted regression models and time-to-event analyses were used to evaluate associations between dysnatremia and outcomes and to assess effect modification by age. Results Among hospitalized adults, both hyponatremia and hypernatremia were associated with significantly worse in-hospital outcomes compared with normonatremia. Hypernatremia demonstrated the strongest associations with mortality and non-routine discharge. Older adults experienced substantially higher absolute risks of mortality and discharge to skilled nursing or long-term acute care facilities, while younger adults exhibited larger relative risk estimates. Significant age–sodium interactions were observed across mortality, discharge disposition, and length of stay, indicating that the impact of dysnatremia differs meaningfully by age group. Conclusions Dysnatremia is strongly associated with increased mortality, prolonged hospitalization, and institutional discharge among hospitalized adults, with older adults bearing the greatest absolute burden of adverse outcomes. These findings highlight dysnatremia as a clinically meaningful marker of vulnerability during hospitalization and underscore the importance of age-specific risk stratification and discharge planning in patients with sodium abnormalities.