The role of electrolytes imbalance in determining poor health outcomes in a cohort of older in-patients: the ELECTROHEALTH study

Electrolyte imbalances are frequent in older adults and may be associated with adverse clinical outcomes. We examined whether admission serum sodium and potassium levels were associated with mortality, rehospitalization, and functional trajectories in geriatric inpatients, distinguishing idiopathic from secondary disturbances. We conducted a retrospective cohort study of patients ≥ 75 years admitted to the acute or rehabilitation geriatric ward of Lausanne University Hospital. Sodium and potassium levels were measured within 24 h of admission. Outcomes included length of stay, early rehospitalization (< 30 days), one-year rehospitalization, all-cause mortality and functional and cognitive assessment. Among 2,575 hospitalizations (mean age 86 years; 66% women), hyponatremia occurred in 15% hypokalemia in 5.9 and hyperkaliemia in 20.1%. In idiopathic cases (n = 1,033), neither hyponatremia nor hypokalemia independently predicted mortality, rehospitalization, or cognitive/functional decline. In contrast, higher potassium at admission was associated with lower one‑year mortality after adjustment for age and sex. (HR = 0.787, p = 0.029). In the full cohort, severe hyponatremia and hypernatremia were associated with advanced age and shorter survival, while hypo- and hyperkalemia were associated with early rehospitalization. Mild idiopathic electrolyte imbalances were not independently associated with adverse outcomes, whereas severe or secondary imbalances appeared to reflect underlying frailty or disease burden. Higher potassium level may indicate better nutritional status and resilience, underscoring the need for further prospective research to clarify its role in healthy aging.