Relationship between serum sodium level within the low-normal range on admission and long-term clinical outcomes in patients with acute decompensated heart failure

Abstract

Although hyponatremia during hospitalization for acute decompensated heart failure (ADHF) is reportedly related with poor prognosis, the available data regarding the impact of serum sodium level within the low-normal range at admission on clinical events in patients with ADHF is limited. We studied eligible patients admitted to our institution in 2007-2011. All the patients were categorized into 3 groups according to the admission serum sodium levels of < 135 mmol/L (hyponatremia), ≥135 and < 140 mmol/L (low-normal range), or ≥140 mmol/L (normal range). The association between admission serum sodium levels and long-term clinical events, a composite of all-cause deaths and re-hospitalizations for ADHF, was assessed by multivariable Cox proportional analysis. Of the 584 eligible patients, 208 (35.6%) were in the low-normal range and 99 (16.9%) had hyponatremia on admission. On multivariable analysis, compared with those with a sodium level ≥140 mmol/L, patients with hyponatremia were at increased risk for clinical events (hazard ratio [HR], 1.53; P = 0.041), whereas the HR of those in the low-normal range was attenuated and insignificant (HR, 1.08; P = 0.625). However, the HR of each category increased significantly as sodium level decreased (P value for HR trend, 0.024). In addition, when serum sodium level was treated as a continuous variable, the lower the serum sodium level, the greater the risk of clinical events (P = 0.012). The cut-off value of serum sodium level to predict mortality was < 138 mmol/L. In conclusion, a low serum sodium level on admission for ADHF, even if low-normal, can increase the risk of long-term mortality and/or re-hospitalization for ADHF.