Renal uric acid clearance in human neonates.

Renal clearance of uric acid was examined in 40 premature and term infants during the first 24 hours of life. Creatinine clearance and uric acid clearance increased with increasing gestational age. Serum uric acid concentration (r = -0.31, P less than 0.05) and fractional excretion of uric acid (r = -0.50, P less than 0.01) were inversely related to gestational age; FEUA was nearly 70% at 29 to 31 weeks gestational age, and decreased to a mean value of 39 +/- 14% (+/- SD) at 38 to 40 weeks gestational age. The decline in FEUA with advancing gestational age appears to represent alterations in net renal tubular transport of uric acid, because the filtered load of uric acid increased with gestational age. Postnatal clearance studies were performed in 18 premature infants of 29 to 35 weeks gestational age; FEUA also declined during early postnatal development (r = -0.44, P less than 0.01). In all studies, a relationship between FEUA and fractional excretion of sodium was observed. The high basal excretion of uric acid in infants may increase the risk of acute uric acid nephropathy when excretion demands are increased.