Effects of sodium urate and uric acid crystals on the crystallization of calcium oxalate.

Crystallization of calcium oxalate in the presence of uric acid and sodium urate crystals was analyzed in a metastable crystallization system containing calcium chloride and sodium oxalate (A), in urine highly supersaturated with respect to calcium oxalate (B), and in urine with a high level of metastable supersaturation (C). In system A uric acid crystals in concentrations up to 11.4 mMol/l did not affect calcium oxalate crystallization, neither did sodium urate during the first 6 h in concentrations below 5 mMol/l. In system B neither uric acid nor sodium urate crystals affected calcium oxalate crystallization. However, an increased rate of crystallization was observed with both uric acid and sodium urate in system C, but the effect was less pronounced than with calcium oxalate seed. Urine pre-treated with sodium urate and subsequently analyzed in system A in a concentration of 2%, gave a slightly lower inhibition of calcium oxalate crystal growth. Concerning the crystal size distribution in the same system, larger crystals were observed in several urines pre-treated with uric acid and sodium urate.