Plasma concentration of BNP according to age (A) in newborn infants from the first to the 14th day of life, and (B) in infants older than two weeks, children, and adolescents. Plasma concentration of BNP according to age (A) in newborn infants from the first to the 14th day of life, and (B) in infants older than two weeks, children, and adolescents. Open circles, boys; grey circles, girls. A Koch, and H Singer Heart 2003;89:875-878 Copyright © BMJ Publishing Group Ltd & British Cardiovascular Society. All rights reserved.