Age dependence of serum beta-N-acetylhexosaminidase (NAG) activity.

Serum N-acetyl-beta-D-glucosaminidase (NAG; EC 3.2.1.30) is a hexosaminidase and may be a predictor of vascular injury, e.g., in infant respiratory distress syndrome, pneumonia, broncho-pulmonary dysplasia and necrotizing enterocolitis. To estimate the new diagnostic prospects we have modified our urinary NAG assay. In this sensitive colorimetric micro-assay, VRA-GlcNAc was used as a substrate. In the present study the age dependence of serum NAG activity was investigated in newborn babies, infants (1-24 months), children (2-18 years) and adults (19-80 years). Serum NAG activity was found to be age-dependent; it is higher in early childhood (11-59 U/l) but decreases to a constant value at the age of 1-2 years. After the age of 2 years it is similar to adults' NAG (10-30 U/l). In pediatrics age-matched reference ranges must be taken into consideration.