Urinary N-acetyl-β-D-glucosaminidase (NAG) and α₁-microglobulin excretion as an index of renal tubular dysfunction in the neonate

The clinical importance of urinary N-acetyl-β-D-glucosaminidase (NAG) and α₁-microglobulin (Protein HC) as markers of impaired renal tubular function was evaluated in 33 preterm newborns (20 males and 13 females) over the first week of life. None of the subjects had congenital or neonatal urinary tract disorders. Eleven newborns without neonatal infections, anoxia, asphyxia, or respiratory distress syndrome (RDS) were considered the control group (group A). Seventeen newborns were treated with ampicillin plus amikacin for suspected bacterial infection (group B), and the remaining five newborns (group C) with asphyxia, but without infections and/or drug administration, were put on mechanical ventilation immediately after birth, for 5 days. Twelve hour urine samples were collected in all infants up to the 6th day of life, and creatinine, NAG, and α₁-microglohulin concentrations were determined. The clinical significance of urinary NAG was found to be different from that of α₁-microglobulin. NAG can be considered an early marker of renal tubular injury, followed by loss of cellular membrane integrity and cytolysis, and α₁-microglobulin an early marker of renal tubular cell dysfunction, characterized by incomplete or inadequate reabsorption of low-M(r) proteins.