N-acetyl-beta-D-glucosaminidase excretion in calcium oxalate stone patients and its relation to the risk of stone formation.

A tubular renal damage induced by crystals in the renal tubuli can be the triggering primary but also secondary cause of stone formation. In 72 calcium oxalate stone patients (45 men, 27 women) N-acetyl-beta-D-glucosaminidase [NAG] excretion in 24h-urine was investigated. 48 healthy test persons (27 men, 21 women) served as a control group and helped to establish reference values. In order to find out a possible relation between NAG reference values and the risks of urolithiasis, lithogenous and inhibitory substances were determined in both groups. In the following, relative calcium oxalate supersaturation, representing a risk of urinary stone formation, was analyzed and compared to NAG excretion values. The threshold value of pathologic NAG excretion was determined in the group of healthy test subjects (mean value +/- 2 standard deviation) and was fixed at 4.2 U/d (women 3.06 U/d, men 4.24 U/d). In our investigations on NAG excretion significantly (p < 0.05) increased values were found in stone patients (4.43 U/d +/- 4.27) as compared to healthy test persons (2.13 U/d +/- 1.02). In the case of increased NAG excretion in stone patients there was a positive correlation between NAG excretion and increased phosphate, sulphate, uric acid, oxalate, and creatinine excretion. Only in female patients there was a relation between relative calcium oxalate supersaturation and NAG excretion values. As a result, NAG determination is considered to be an appropriate means of tracing a certain risk group within calcium oxalate stone patients.