Lithogenic risk factors in the urine of black and white subjects

Objective To identify biochemical and dietary factors which may play a role in the low incidence of stone formation in the black South African populat ion. Subjects and methods The study included 31 semi-urbanized black and 29 urba nized white subjects. The protocol and modern laboratory techniques used to assess recurrent stone formers were followed, Urinary sodium, potassium, c reatinine, calcium, phosphate and urate levels were measured, and urinary c itrate, oxalate and cystine assessed, Results Black subjects ate a diet significantly higher in sodium (P<0.04); there was no difference in serum levels but urinary sodium was significantl y higher (P<0.001) in black than in white subjects. Urinary potassium, calc ium, citrate, phosphate and cystine were all significantly lower in black t han in white subjects (P<0.001 for the first four and P<0.03 for cystine), Conclusion Certain intrinsic factors in South African black subjects may ac count for their lower frequency of stone formation than in white subjects. Of these, the very low urinary calcium, decreased urinary cystine and diffe rent interactions between sodium and calcium/cystine are probably important .