Objectives: This study sought to compare the renal clearance mechanisms of B-type natriuretic peptide (BNP) and amino terminal pro-B-type natriuretic peptide (NT-proBNP).
Background: The small molecular weight proteins (SMWPs) BNP and NT-proBNP both inversely correlate with glomerular filtration rate (GFR). Whether this association is causal or confounding is unknown and has been the basis of widespread speculation.
Methods: We combined measurements of BNP and NT-proBNP concentrations in the renal arteries and veins of 165 subjects undergoing renal arteriography with invasive renal plasma flow (RPF) measurements and echocardiography. Fractional extraction (FE) of BNP and NT-proBNP was computed.
Results: The BNP and NT-proBNP concentrations correlated similarly to GFR (r = -0.35 and r = -0.30, respectively; p < 0.001 for both) but the NT-proBNP/BNP serum ratio was negatively associated with GFR (r = -0.21, p = 0.008). Median FE(BNP) was 0.21 (interquartile range [IQR] 0.16 to 0.22) for left and 0.22 (IQR 0.17 to 0.29) for right kidneys. Median FE(NT-proBNP) was 0.16 (IQR 0.09 to 20) for left and 0.18 (IQR 0.12 to 0.22) for right kidneys. The FE(BNP) correlated with GFR (left: r = 0.26, p = 0.008; right: r = 0.21, p = 0.03) as did FE(NT-proBNP) (left: r = 0.25, p = 0.005; right: r = 0.20, p = 0.02). Although FE(BNP) and FE(NT-proBNP) correlated strongly with each other (left: r = 0.66; right: r = 0.60; p < 0.001 for both), left and right FE(NT-proBNP/BNP) ratios were not influenced by GFR (r = 0.10, p = 0.30 and r = 0.08, p = 0.43, respectively). Multivariate analyses confirmed that FE was not independently associated with BNP or NT-proBNP concentrations.
Conclusions: Contrary to widespread belief (but in line with the renal physiology of SMWP), BNP and NT-proBNP are equally dependent on renal function for their clearance.