Background: Urinary excretion is currently regarded as the main mechanism of elimination of N-terminal prohormone brain natriuretic peptide (NT-proBNP). The clinical implications and the value of measurement of urinary NT-proBNP in patients with heart failure are largely unknown.
Methods and results: We studied 94 patients (age, 58+/-11 years; 79% men) with chronic heart failure (CHF) and 20 age- and sex-matched healthy control subjects. Glomerular filtration rate and effective renal plasma flow were measured as clearance of (125)I-iothalamate and (131)I-hippuran, respectively. NT-proBNP levels were determined in both plasma and 24-hour urine collections. Mean left ventricular ejection fraction of CHF patients was 0.28+/-0.09. Plasma NT-proBNP levels were higher in CHF patients compared with control subjects (median, 547 versus 41 pg/mL; P<0.001). Urinary NT-proBNP excretion, however, was substantially lower in CHF patients (median, 0.13 versus 2.3 mL/min; P<0.001). Urinary NT-proBNP excretion was independent of estimated glomerular filtration rate. In both CHF patients and control subjects, there was a strong and inverse relation between plasma NT-proBNP concentrations and urinary NT-proBNP excretion (r=-0.72 and r=-0.65 respectively; both P<0.001). Decreased renal plasma flow in CHF was significantly associated with a lower excretion of NT-proBNP (P=0.026).
Conclusions: Urinary NT-proBNP excretion is lower in patients with CHF compared with control subjects and is inversely related to plasma NT-proBNP. Urinary NT-proBNP is associated with renal plasma flow but not with estimated glomerular filtration rate. Elevated levels of plasma NT-proBNP in patients with CHF might be explained not only by myocardial stress but also by a marked decrease in urinary excretion.