Abstract 5948: Lower Urinary NT-proBNP Excretion in Patients with Chronic Heart Failure
Introduction: Elevation of NT-proBNP in chronic heart failure (CHF) is considered to be caused by release from the ventricles in response to myocardial stress. Urinary excretion is currently regarded as the main mechanism of elimination of NT-proBNP. The precise mechanism of renal handling of this peptide in patients with heart failure, however, is largely unknown.
Hypothesis: We assessed the hypothesis that part of the elevated concentrations of plasma NT-proBNP levels in CHF is related to impaired renal function.
Methods: We studied 94 patients with CHF and 20 age and gender matched healthy controls. Estimated glomerular filtration rate (eGFR) was calculated using the sMDRD formula. In addition, in the CHF patients glomerular filtration rate (GFR) and effective renal plasma flow were measured as clearance of 125I-iothalamate and 131I-Hippuran, respectively. NT-proBNP levels were determined in both plasma and 24-hour urine collections.
Results: CHF patients were 58±11 years, 79% were male, mean eGFR was 64±17 mL/min/1.73 m2 and mean left ventricular ejection fraction (LVEF) 28±9%. Control subjects were 58±4 years, 80% were male, and mean eGFR was 90±12 mL/min.1.73 m2. Plasma NT-proBNP levels of CHF-patients were higher compared to controls (median 547 (IQR 253–1,324) pg/ml) versus 41 (IQR 28 – 69) pg/mL, P<0.001). However, urinary NT-proBNP-excretion was substantially lower in CHF-patients versus control subjects, median 0.13 (IQR 0.04 – 0.32) versus 2.3 (IQR 1.1–3.6) mL/min, P<0.001). This was independent of the difference in eGFR between CHF patients and controls. We found a strong and inverse relation between plasma NT-proBNP concentrations and urinary NT-proBNP excretion. A decreased renal plasma flow in CHF was associated with a lower excretion of NT-proBNP (r=0.25, P=0.017).
Conclusions: Elevated plasma NT-proBNP concentrations in patients with CHF are not only explained by myocardial stress, but also by a marked decrease in urinary excretion. The decrease in NT-proBNP excretion is highly disproportional to eGFR, suggesting that reduced renal blood flow affects tubular handling.