SUMMARY Urinary N-acetyl-beta-glucosaminidase (NAG) excretion was measured in 14 healthy, preterm, male neonates with gestational ages between 32 and 35 weeks. Daily NAG excretion increased significantly during the first four weeks of life. No correlation was observed between urinary NAG:creatinine ratio and postnatal age regardless of whether measurements were taken from the whole 24 hour urine collection or from an isolated urine spot sample at fhe same time on each day. When the preterm infants were compared with a group of 20 healthy, full term, male infants at a postnatal age of 7 days the NAG:creatinine ratio was significantly higher in the preterm group, the measurements having been taken from single urine spot samples. We suggest that this variable be used in the evaluation of renal tubular integrity during the neonatal period.Renal anatomic integrity can be reflected in the output of urinary enzymes.' Of these enzymes, N-acetyl-beta-glucosaminidase (NAG) may be of greatest interest as it is present in appreciable amounts in the proximal tubular cells.2 The molecular weight of NAG is about 140 000 daltons.3 Enzymes with molecular weights that exceed 70 000 daltons are not normally filtered into the urine.4Increased urinary excretion of NAG has been found to be correlated with tubular damage in children with a variety of renal diseases.5 6 In adults urinary excretion of NAG has been shown to be a good predictor of aminoglycoside toxicity to the tubular epithelium.7 Few data are available on the urinary excretion of NAG in neonates who present with renal damage.5 6 8 9 Parini et al used NAG excretion in the neonatal period as a predictor of possible renal toxicity during treatment with amikacin. They gave no information, however, about the normal excretion of this enzyme in growing preterm newborns.'0 The purpose of this study was to measure the urinary excretion of this lysosomal enzyme in healthy preterm babies and to investigate whether the urinary NAG excretion is influenced by postnatal age.
Patients and methodsRenal function and urinary NAG excretion were evaluated in 14 healthy neonates whose gestational ages were between 32 and 35 weeks. " Gestational age was assessed according to the Finnstrom score. 12 Only male infants were recruited due to the difficulties in obtaining precise 24 hour urine collections in girls. Infants were excluded if they had any of the following conditions: nephrotoxic drugs administered to the mother during the final trimester, Apgar score below 7 at one minute, respiratory distress syndrome, infectious diseases, any drugs in the neonatal period, episodes of hypotension or hypertension according to Bucci's criteria, serum bilirubin concentration >206 ismol/l, and patent ductus arteriosus. Fluids were administered as follows: 60 ml/kg/day on day 1, 80 ml/kg/day on day 2, 100 ml/kg/day on day 4, 130 ml/kg/day on day 6, and 150-180 ml/kg/day from day 8 onwards. Parenteral fluids (10% dextrose and electrolytes) were given from day 1 to day 5. A formula adapted for preterm neon...
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