[Urinary N-acetyl-beta-D-glucosaminidase activity in healthy, polycythemic and hypoxic newborn infants].

Urinary N-acetyl-beta-D-glucosaminidase (NAG) activity was assayed in 20 polycythemic newborns and prematures, together with 50 prematures suffering from hypoxia on the 1st, 2nd, 4th, 14th, and 28th day after birth. The enzyme was also assayed in 101 healthy newborns which provided normal reference values. NAG activity was factored by the creatinine concentration to given an index. There were significant difference in the NAG indices either between full-term and preterm babies or between appropriate for gestational age (AGA) and small for gestational age (SGA) neonates of the normal group. However, NAG excretion on the first day of life was significantly raised in the case of polycythemic newborns. Following partial plasma exchange, on the 14th day the NAG activity returned to the normal range. NAG activities of premature babies suffering from idiopathic respiratory distress syndrome (IRDS) were significantly elevated on the 1st, 2nd, 4th day but fell sharply to the 14th day. NAG activity fell to normal values by the 28th day. These results suggest that the urinary NAG index is a sensitive indicator of the renal tubular damage during the newborn period.