Early Spot Urinary Sodium and Diuretic Efficiency in Acute Heart Failure and Concomitant Renal Dysfunction

OBJECTIVE In acute heart failure (AHF), early assessment of spot urinary sodium (UNa) has emerged as a useful biomarker for risk stratification and monitoring. The objective of this study was to investigate (a) whether early spot UNa predicts 24-h diuretic efficiency and (b) the clinical factors associated with early spot UNa in patients with AHF and concomitant renal dysfunction (RD). METHODS This is a post hoc analysis of the IMPROVE-HF trial, in which 160 patients with AHF and RD (estimated glomerular filtrate rate [eGFR] <60 mL/min/1.73 m2) were included. Diuretic efficiency was calculated as the net fluid output produced per 40 mg of furosemide equivalents in 24 h. The association between early spot UNa and diuretic efficiency and clinical variables associated with UNa were evaluated using multivariate linear regression analysis. The contribution of the exposures in the predictability of the models was assessed with the coefficient of determination (R2). RESULTS The mean age of the study population was 78 ± 8 years. The median (interquartile range) diuretic efficiency, early spot UNa, aminoterminal pro-brain natriuretic peptide, and eGFR were 747 (490-1,167) mL, 90 mmol/L (65-111), 7,765 pg/mL (3,526-15,369), and 33.7 ± 11.3 mL/min/1.73 m2, respectively. In a multivariate setting, lower UNa was significantly and nonlinearly associated with lower diuretic efficiency (p = 0.001), explaining the 44.4% of the model predictability. Natremia and surrogates of congestion emerged as the main factors related to UNa. CONCLUSIONS In patients with AHF and RD at presentation, early spot UNa was inversely related to 24-h diuretic efficiency.