Objective. The purpose of the study was to examine the possible age dependency of plasma N-terminal pro atrial natriuretic peptide (N-ANP) and N-terminal pro brain natriuretic peptide (N-BNP) levels in healthy term neonates to establish normal ranges for the neonatal period.

Methods. N-ANP and N-BNP plasma concentrations were measured in peripheral venous (n = 116) and umbilical cord blood (n = 37) in 153 healthy term neonates (mean: 5.1; range: 0–30 days) using an enzyme immunoassay. The neonates were classified into 8 groups according to their age (day of delivery and 1, 2, 3, 4, 5–7, 8–14, and 14–30 days of age).

Results. The plasma N-ANP and N-BNP concentration were the highest at the first day of age (96 700; 6912–436 000 and 641; 254-1272 fmol/mL) and were found significantly higher compared with the day of delivery (5680; 1005–16 900 and 221; 58–478 fmol/mL; P < 0,0001). After this marked increase, N-ANP and N-BNP levels decreased steadily and became stable at the fifth (5232; 2691–7353 fmol/mL) and third (246; 110–430 fmol/mL) day of life, respectively.

Conclusions. The N-ANP and N-BNP plasma concentrations in healthy neonates showed a marked increase during the first days of age, suggesting that ANP and BNP have physiologic roles in the perinatal circulatory change from fetus to neonate.

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