Urinary excretion of N-acetyl-glucosaminidase after extracorporeal shockwave lithotripsy : a marker of renal tubule injury

The major complications of extracorporeal shock wave lithotripsy (ESWL) are perirenal hematomas for an incidence of less than 1 per cent. However in animal experiments histopathological effects of focused electrohydraulic shock waves on renal parenchyma have been reported, the most significant of which are hemorrhagic foci healing rapidly by cicatrization. Furthermore imaging studies have demonstrated morphological changes limited to the area of the kidney exposed to shock waves. Liver, skeletal muscle and pancreatic enzyme changes have been documented after ESWL. In our experience the urinary ratio of NAG (N-acetyl-glucosaminidase) to creatinine, a good marker of renal tubular damage, increased after treatment with both the original and the modified spark gap Dornier HM3 lithotripters and with the piezoelectric Wolf Piezolith 2200. Particularly the threshold of pathological urinary NAG excretion were 2,000 and 2,600 shocks respectively using the original and the modified Dornier HM3 and 7,000 shocks using the Wolf Piezolith 2200. The functional significance of the changes is not known, however in clinical practice it would seem prudent to avoid excessive exposure to shock waves.