How does hyperuricosuria contribute to renal stones?
Uric acid stones develop in approximately 25% of patients with symptomatic tophaceous gout. Excessive urinary uric acid (> 600 mg/day) supersaturates the urine, crystallizes, and forms uric acid stones. However, most uric acid stone formers do not have gout, hyperuricemia, or hyperuricosuria. But all have a urinary pH < 5.5, which promotes uric acid stone formation. Approximately 25% of calcium stone formers have hyperuricosuria. Hyperuricosuria decreases the solubility of calcium oxalate. Monosodium urate may interfere with inhibitors, resulting in increased calcium oxalate stone formation. This disorder, called hyperuricosuric calcium nephrolithiasis, is characterized by normal serum calcium, urinary uric acid > 600 mg/day, urine pH > 5.5, and recurrent calcium stones.