Effects of human urine on aggregation of calcium oxalate crystals

The importance of aggregation in calcium oxalate urolithiasis, although not fully understood, has long been postulated. Previous investigators of calcium oxalate crystal aggregation have applied static crystallization rather than continuous flow techniques to their studies. We describe the use of a Couette agglomerator in series with our previously reported continuous flow mixed suspension-mixed product removal crystallization system. We compared synthetic urine controls with 5 per cent volume-in-volume human urine additions from normal persons or patients with calcium oxalate stones. There was no significant difference in nucleation, linear crystal growth rate or total crystal mass between normal persons and those with stones. Control nucleation rate was significantly higher than in either human urine addition group. Comparison of aggregator particle size distributions revealed significant differences in aggregation among the control, normal and stone groups. We concluded that urine inhibitors to aggregation are somewhat deficient in patients with stones, resulting in the generation of larger particle masses or eventually stones.