Uric acid nephrolithiasis: Basic and clinical aspects

Of the kidney-stone-forming population, 8�10 % are comprised of uric acid nephrolithiasis. The major pathophysiologic mechanism for uric acid stone formation is unduly acidic urine. At a urinary pH below 5.0, the concentration of sparingly soluble uric acid increases and promotes uric acid precipitation. Unduly acidic urine is likely due to decreased ammonium excretion and/or increased endogenous acid production. The underlying mechanism of these abnormalities has been linked to the metabolic syndrome but may also be associated with renal fat accumulation in the kidney (lipotoxicity). Although low urinary pH is necessary, it alone may not be suf fi cient to cause uric acid crystallization. Therefore, it is plausible that the lack of an inhibitor or the presence of a promoter of stone formation may play a role in uric acid nephrolithiasis.