Relationship between admission serum sodium concentration and clinical outcomes in patients hospitalized for heart failure: an analysis from the OPTIMIZE-HF registry

Aims Hyponatraemia has been shown to be an independent predictor of mortality in selected patients with heart failure enrolled in clinical trials. The predictive value of hyponatraemia has not been evaluated in unselected patients hospitalized with heart failure. Methods and results OPTIMIZE-HF is a registry and performance-improvement programme for patients hospitalized with heart failure and includes a subgroup with 60-90 day follow-up data. The relationship between admission serum sodium concentration and clinical outcomes was analysed in 48 612 patients from 259 hospitals. Admission serum sodium levels were analysed both as a continuous variable and by grouping patients with admission Na < 135 and Na >= 135 mmol/L. Patients with hyponatraemia (Na < 135 mmol/L) at the time of hospital admission had modest differences in baseline clinical characteristics and management during hospitalization compared with patients who had serum sodium >= 135 mmol/L. Patients with hyponatraemia were more likely to be Caucasian, have lower admission systolic blood pressure, and receive intravenous inotropes during hospitalization. Patients with hyponatraemia had significantly higher rates of in-hospital and follow-up mortality and longer hospital stays, although no difference in re-admission rates was observed. After adjusting for differences with multivariable analysis, the risk of in-hospital death increased by 19.5%, the risk of follow-up mortality by 10%, and the risk of death or rehospitalization by 8% for each 3 mmol/L decrease in admission serum sodium below 140 mmol/L. Conclusion Hyponatraemia in hospitalized patients with heart failure is relatively common and is associated with longer hospital stays and higher in-hospital and early post-discharge mortality. Re-admission rates were equally high in patients with or without hyponatraemia.