Crystalluria and urolithiasis in a relatively stone-free population.

The occurrence of renal stone in South African blacks is extremely rare. Whites however are prone to calculi to the same extent as that reported in other Western communities. The nature of the particulate material and crystalluria in urine samples from the two population groups were investigated using a Coulter Counter and scanning electron microscope. In addition, 10 calculi obtained from black patients over a 5 year period were analysed. The particle size distribution curves obtained for normal black and white males were identical. The curves for normal black and white females were also identical but different from those for males. Black male stone formers had larger particles than their controls while the single black female stone former investigated had particles of the same size as female controls, but in greater numbers. Scanning electron microscopy revealed profuse amounts of crystalline NaCl, KCl and other salts in the urinary sediments of blacks. These were not observed in the specimens from whites nor in the black stone formers' urines. Analysis of the calculi identified chemical and ultrastructural features similar to those observed in stones from whites. The hypothesis that the lower incidence of stone disease in blacks may be due to a high Na/Ca ratio is supported by our findings. It is suggested that various salts play a role in lowering the stone forming potential of such urines by a competitive substitution mechanism in which lattice calcium is displaced by sodium. It is also suggested that when urinary stone formation does occur in blacks, it does so via the same physicochemical mechanisms as in any other race group.