Relationship Between Serum Sodium Level Within the Low-Normal Range on Admission and Long-Term Clinical Outcomes in Patients with Acute Decompensated Heart Failure

: 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.