Uric acid nephrolithiasis: current concepts and controversies.

PURPOSE

Uric acid calculi with or without a calcium component comprise a significant proportion of urinary stones. Knowledge of the pathophysiology of stone formation is important to direct medical treatment. The aim of this review is to provide an update on the epidemiology, pathophysiology and management of uric acid renal stones.

MATERIALS AND METHODS

A MEDLINE search was performed on the topic of uric acid stones. Current literature was reviewed with regard to the epidemiology, pathophysiology, associated medical conditions and management of uric acid stones.

RESULTS

The incidence of uric acid stones varies between countries and accounts for 5% to 40% of all urinary calculi. Hyperuricuria, low urinary output and acidic urine are well known contributing factors. However, the most important factor for uric acid stone formation is persistently acidic urine. Gout and myeloproliferative disorders are associated with uric acid stones. Why most patients with gout present with acidic urine yet only 20% have uric acid stone formation remains unclear. The pathophysiological basis for persistent urine acidity also remains unclear although various mechanisms have been proposed. Urinary alkalization with potassium citrate or sodium bicarbonate is a highly effective treatment, resulting in dissolution of existing stones and prevention of recurrence.

CONCLUSIONS

Acidic urine is a prerequisite for uric acid stone formation and growth. Medical management with urinary alkalization for stone dissolution and prevention of recurrence is effective and should be the cornerstone of treatment.