Relationship between undissociated uric acid, total uric acid, and urinary pH

The limit of solubility of undissociated uric acid is depicted by the dotted line (approximately 100 mg/L). Two hypothetical urine pHs are considered (two arrows). At low urinary pH (eg, 5.0), even a modest amount of total urinary uric acid will exceed its solubility. At high urine pH (eg, 6.5), even massive hyperuricosuria is well tolerated.