Increased urinary excretion of renal N-acetyl-beta-glucosaminidase in hypercalciuria.

Urinary excretion of N-acetyl-beta-glucosaminidase (NAG), a lysosomal enzyme, was examined in 33 children with hypercalciuria. Urinary NAG excretion in 13 healthy children was 5.84 +/- 9.35 nmole/hr/mg of creatinine (NAG/Cr) (mean +/- SD) compared with 35.61 +/- 42.04 nmole/hr/mg of creatinine in 23 children with renal hypercalciuria, and 28.99 +/- 13.69 nmole/hr/mg of creatinine in ten children with absorptive hypercalciuria. In children with renal hypercalciuria, NAG/Cr excretion was not statistically different between children with either urolithiasis or hematuria without calculi. In six children with renal hypercalciuria, no significant change in NAG/Cr excretion occurred after a mean duration of 25 weeks of hydrochlorothiazide therapy although urinary calcium to creatinine ratios (UCa/Cr) decreased from 0.24 +/- 0.11 to 0.16 +/- 0.11. We conclude that increased urinary calcium excretion produces renal tubular injury and that the renal injury may not be reversed by short-term alterations in urinary calcium excretion.