Fractional excretion of sodium predicts worsening renal function in acute decompensated heart failure

BACKGROUND: Renal impairment (RI), defined as an increase in creatinine level of greater than 26.5 mmol/L, develops in more than 30% of acute decompensated heart failure (ADHF) patients. Fractional excretion of sodium (FeNa) reflects sodium handling by the kidneys during diuresis. AIM: To study the relationship between FeNa and RI in patients admitted with ADHF. METHOD: The hospital course and renal function of all ADHF patients admitted to the hospital were prospectively observed. Patients were included if their admission creatinine level was 176 mmol/L or lower, they had been on a low-salt diet since admission, had urine sodium and creatinine samples collected more than 6 h after a furosemide dose in the first few days of admission, and they were on daily intravenous furosemide doses of 20 mg or more. RESULTS: Over six months, 51 patients met the inclusion criteria; the average daily dose of intravenous furosemide was 58.8 mg. RI developed in 39% of patients. A FeNa cut-off point of 0.4% was determined using ROC curve analysis; patients with a FeNa of greater than 0.4% (28 patients) were compared with patients with a lower FeNa (23 patients). Admission creatinine level and furosemide dose were higher in the first group (P=0.01 and P=0.06, respectively). The first group developed RI more frequently (OR=6.3; 95% CI 1.7 to 23.5; P=0.0047; adjusted OR for admission creatinine =6.18; 95% CI 1.6 to 24.5; P=0.0096; and adjusted OR for furosemide dose = 4.7; 95% CI 1.3 to 16.7; P=0.016). They had a longer hospitalization course (median nine days [interquartile range 6.3 to 13.5 days] versus seven days [interquartile range 4.0 to 9.0 days]; P=0.036) and they were admitted to the cardiac care unit more frequently (OR=6.8; 95% CI 1.3 to 34.9; P=0.02). CONCLUSION: A FeNa of greater than 0.4% more than 6 h after a dose of diuretics predicts RI and a complicated hospital course in ADHF patients.