Risk of Adverse Clinical Outcomes in Hyponatremic Adult Patients Hospitalized for Acute Medical Conditions: A Population-Based Cohort Study

Context: Hyponatremia has been associated with excess long-term morbidity and mortality. However, effects during hospitalization are poorly studied. Objective: The objective of this work is to examine the association of hyponatremia with the risk of in-hospital mortality, 30-day readmission, and other short-term adverse events among medical inpatients. Design and Setting: A population-based cohort study was conducted using a Swiss claims database of medical inpatients from January 2012 to December 2017 Patients: Hyponatremic patients were 1:1 propensity-score matched with normonatremic medical inpatients. Main Outcome Measure: The primary outcome was a composite of all-cause in-hospital mortality and 30-day hospital readmission. Secondary outcomes were intensive care unit (ICU) admission, intubation rate, length-of-hospital stay (LOS), and patient disposition after discharge. Results: After matching, 94 352 patients were included in the cohort. Among 47 176 patients with hyponatremia, 8383 (17.8%) reached the primary outcome compared with 7994 (17.0%) in the matched control group (odds ratio [OR] 1.06 [95% CI, 1.02-1.10], P= .001). Hyponatremic patients were more likely to be admitted to the ICU (OR 1.43 [95% CI, 1.37-1.50], P< .001), faced a 56% increase in prolonged LOS (95% CI, 1.52-1.60, P< .001), and were admitted more often to a postacute care facility (OR 1.38 [95% CI 1.34-1.42, P< .001). Of note, patients with the syndrome of inappropriate antidiuresis (SIAD) had lower in-hospital mortality (OR 0.67 [95% CI, 0.56-0.80], P< .001) as compared with matched normonatremic controls. Conclusion: In this study, hyponatremia was associated with increased risk of short-term adverse events, primarily driven by higher readmission rates, which was consistent among all outcomes except for decreased in-hospital mortality in SIAD patients.