N-Acetyl-β-d-glucosaminidase (NAG) and NAG isoenzymes in children with upper and lower urinary tract infections

The use of N-acetyl-β-d-glucosaminidase (NAG) to diagnose the site of urinary tract infection was studied in pediatric patients. Differentiation between upper and lower tract infections (UTI) was based on clinical grounds and on elevated erythrocyte sedimentation rate, C-reactive protein and fever. NAG excretion expressed as nmol · h⁻¹ · mg⁻ of urinary creatinine was higher in children with upper UTI (mean ± SE 906 ± 236) than in those with lower UTI (145 ± 23) or healthy children (151.6 ± 10) (p<0.01 by Duncan's test). In children with upper UTI, NAG excretion fell in parallel with the remission due to antibiotic treatment. This however was not seen in children treated with aminoglycosides. A specific and significant elevation (p < 0.01) of the B isoenzyme of NAG was documented in children with upper UTI but not in those with lower UTI (B form in upper UTI 49.2% ± 3.9 versus 21.9 ± 3.3 in lower UTI; healthy children 18.9 ± 3.4). The percentage of B isoenzyme excreted was high in two children with upper UTI but was low total NAG urinary excretion, suggesting that the quantification of isoenzymes offers further specificity in diagnosis. We conclude that the measurement of NAG and its isoenzymes in children with UTI provides useful information in the diagnosis of the site of infection.