[Diagnosis and prevention of uric acid stones].

Uric acid stones occur in 10% of all kidney stones and are the second most-common cause of urinary stones after calcium oxalate and calcium phosphate calculi. The most important risk factor for uric acid crystallization and stone formation is a low urine pH (below 5.5) rather than an increased urinary uric acid excretion. Main causes of low urine pH are tubular disorders (including gout), chronic diarrhea or severe dehydration. Uric acid stone disease can be prevented and these are one of the few urinary tract stones that can be dissolved successfully. The treatment of uric acid stones consists not only of hydration (urine volume above 2000 ml daily), but mainly of urine alkalinization to pH values between 6.2 and 6.8. Urinary alkalization with potassium citrate or sodium bicarbonate is a highly effective treatment, resulting in dissolution of existing stones. Urinary uric acid excretion can be reduced by a low-purine diet. Potassium citrate is the treatment of choice for the prevention of recurrence of uric acid calculi. Allopurinol reduces the frequency of stone formation in hyperuricosuric patients with recurrent uric acid stones and/or gout.