Reference values for N-terminal pro-B-type natriuretic peptide in umbilical cord blood.

Plasma concentrations of B-type na-triuretic peptide (BNP), a 32-amino acid peptide hormone secreted by the myocardium, increase in response to myocardial stretch or strain (1, 2). On secretion, proBNP, the storage form of BNP, is cleaved into the inactive N-terminal proBNP (NT-proBNP) and the endocrinologi-cally active BNP. In patients with heart failure, plasma BNP concentrations are related to the severity of symptoms and underlying cardiac abnormality (3). It is also known that neonates show transient increases in both plasma NT-proBNP and BNP in the first days of life as a result of the increased left ventricular volume load induced by the circulatory changes after birth (4). After closure of the duc-tus arteriosus and the foramen ovale and stabilization of the forced circulatory change, plasma NT-proBNP and BNP concentrations are still increased but decrease to " adult " values in the following months (5). Although a small study was published on NT-proBNP and fetal heart rate abnormalities (6), little is known regarding umbilical cord blood BNP or NT-proBNP concentrations. The purpose of the present study was to establish reference values for NT-proBNP concentrations in umbilical cord blood. Of the 71 successively born neo-nates enrolled in the study, 67 were delivered by vaginal delivery and 4 by cesarean section. Gestational age ranged from 32 to 42 weeks. After early clamping of the cord, blood was drawn from the arterial and ve-nous umbilical cord vessels. NT-proBNP was measured with an elec-trochemiluminescence immunoassay (Elecsys ® 2010; Roche). Mean (SD) NT-proBNP concentrations were 79.5 (42.9) and 79.9 (45.0) pmol/L for arterial and venous umbilical cord blood, respectively. NT-proBNP concentrations in arterial and venous umbilical cord blood, plotted against each other, are shown in Fig. 1. There was no significant mean difference in NT-proBNP concentrations between arterial and ve-nous umbilical cord blood (paired-sample t-test). In the studied group of newborns, we found no influence of gestational age, umbilical cord pH, or mode of delivery on NT-proBNP concentrations in the umbilical cord. The maternal NT-proBNP concentration was measured in eight cases and appeared to be within the adult reference interval. In all cases, large differences were found between maternal and neonatal NT-proBNP concentrations , suggesting no placental exchange of NT-proBNP. The high concentrations of NT-proBNP in umbilical cord blood compared with the reference interval for healthy adults (0 –10 pmol/L) might be explained by the differences in cardiac output and ventricular stroke volume. The ventricular volume loads …