Departments of Metabolism and of Clinical Biochemistry

Key words: Gout; Diagnosis of uric acid lithiasis; Treatment of uric acid lithiasis; Uric acid lithiasis; Uric acid metabolism; Uric acid solubility; 2 2 ABSTRACT: Uric acid is the end-product of purine nucleotide metabolism in man. The renal handling of urate is a complicated process, resulting in a fractional clearance of 8.2-10.3 %. The anhydrous form is thermodynamically the most stable uric acid crystal. Uric acid is a weak acid that ionizes with a Pka at pH 5.75. At the normal acidic region, uric acid solubility is strongly increased by urinary pH. The prevalence of uric acid stones varies between the countries, reflecting climatic, dietary, and ethnical differences, ranging from 2.1 % (in Texas), to 37.7 % (in Iran). The risk for uric acid stone formation correlates with the degree of uric acid supersaturation in the urine, depending on uric acid concentration and urinary pH. Hyperuricosuria is the major risk factor, the most common cause being increased purine intake in the diet. Acquired and hereditary diseases accompanied by hyperuricosuria and stone disease include: gout, in strong correlation with the amount of uric acid excreted, myelo an