Hyperuricosuric calcium urolithiasis

Hyperuricosuric calcium urolithiasis is a condition of mixed calcium oxalate stones characterized by hyperuricosuria either in isolation or in conjunction with other risk factors for calcium oxalate stones such as hypercalciuria, hyperoxaluria, and hypocitraturia. There are three proposed physicochemical models of pathogenesis where urate in its crystalline phase via heterogeneous nucleation, in its colloidal phase via removal of crystallization inhibitors, and in solution via precipitation crystallization, can all increase propensity to calcium oxalate precipitation. Regardless of the model, the phenomenologic observation of urate increasing calcium oxalate precipitation appears solid. Another supporting factor are retrospective data analysis and prospective trials showing uric acid lowering reduces stones events in hyperuricosuric calcium stone formers. Due to the heterogeneity of pathogenesis of calcium oxalate stones in the unselected stone-formers, association cannot be demonstrated between uric acid excretion rate and risk of kidney stone the general population. In calcium oxalate stoners with isolated hyperuricosuria or hyperuricosuria in combination with other calcium stone risks where treatment of these traditional risks fails to reduce stone formation, urate acid lowering should be cautiously attempted. More refinement of pathogenic models and prospective controlled trials in phenotypically defined subgroups of subjects with calcium oxalate urolithiasis will be informative.