The effect of seed crystals on calcium oxalate nucleation

Equimolar concentrations of calcium chloride and potassium oxalate were precipitated by a rapid mixing technique. The precipitated calcium oxalate particles were repeatedly counted at 15 min with a Coulter counter until reproducible total particle count and particle distribution curves were obtained. These values were compared with those found after the addition of various seed crystals and 10 per cent urine to the system. Calcium oxalate seed crystals markedly enhanced the nucleation rate of calcium oxalate (1), although only an estimated 16 per cent acted as effective nucleators. The addition of sodium acid urate crystals resulted in a small decrease in the number of calcium oxalate particles precipitated and fewer than 0.1 per cent of the crystals acted as effective nuclei. Seeds of agglomerated hydroxyapatite crystals also produced a small decrease in the number of calcium oxalate particles and fewer than 1 per cent of the seeds functioned as nucleators. The addition of 10 per cent urine to the system greatly increased the number of calcium oxalate particles produced although we are uncertain whether the urine provided effective nuclei or prevented particle aggregation. Our data indicate that, in a rapidly mixed system, neither sodium acid urate nor hydroxyapatite crystals are effective nucleators for the precipitation of calcium oxalate. The occurrence of epitaxial growth of calcium oxalate on these substances in urinary stones is therefore called into question.