Pathophysiology of stone formation.

Urinary stone disease is a multifactorial disorder arising essentially from an abnormal combination of a number of urinary risk factors. In the case of calcium urolithiasis the main risk factors are a low urine volume, a high urinary pH, increased excretions of calcium, oxalate and uric acid and a low net level of inhibitory activity against the crystallization of calcium salts. The last mentioned, in turn, is dependent on the balance between the macromolecular inhibitors, including glycosaminoglycans, ribonucleic acid and acidic glycoproteins, and the promoters of crystallization such as Tamm-Horsfall mucoprotein. There is currently some debate as to whether or not an immunological factor might also be involved in the renal tubules, which results in crystals becoming bound to the renal epithelium.