RENAL-FUNCTION IN PRETERM NEONATES

The plasma creatinine concentration is elevated at birth and decreases concomitantly with the rapid increase in glomerular filtration rate t hat occurs in the first postnatal weeks. The velocity of these changes was assessed during the first 3 wk of life of 66 term and preterm inf ants. The plasma creatinine concentration, creatinine clearance, and s odium fractional excretion were measured serially at weekly intervals, starting 1-4 d after birth [mean = 1.5 +/- 0.8 (SD) d]. Premature inf ants were separated into three groups according to their birth weight: group 1, 1001 to 1500 g; group 2, 1501 to 2000 g; and group 3, 2001 t o 2500 g. Group 4 included 28 term infants (mean birth weight = 3165 /- 78 g). Mean gestational ages in the preterm groups were 31.3, 32.8, and 34.4 wk in groups 1, 2, and 3, respectively. The plasma creatinin e concentration on d 1.5 was significantly higher in preterm (91 +/- 4 mu mol/L) compared with term infants (66 +/- 3 mu mol/L). The differe nces in plasma creatinine were still present during the second week of life, with values of 64 +/- 5, 58 +/- 7, 47 +/- 8, and 40 +/- 4 mu mo l/L in groups 1, 2, 3, and 4, respectively. The difference vanished by d 22-23. On d 1.5, creatinine clearance correlated positively with ge stational age, amounting to 0.65 +/- 0.14, 0.92 +/- 0.19, 1.42 +/- 0.3 1, and 3.36 +/- 0.32 mL/min in groups 1, 2, 3, and 4, respectively. Cr eatinine clearance increased rapidly with postnatal age, the velocity of the maturation being less marked in the most premature infants. The fractional excretion of sodium was significantly higher in the most p remature infants, with values of 2.0 +/- 0.3, 2.2 +/- 0.5, 1.1 +/- 0.2 , and 0.3 +/- 0.1% in groups 1, 2, 3, and 3, respectively. The differe nces vanished by the third week of life. The negative correlation betw een plasma creatinine on d 1.5 and gestational age suggests that the n eonate's creatinine plasma concentration does not simply reflect the m other's plasma concentration.