Comparison of urinary risk factors for calcium kidney stones in South African black and white subjects is a strategic approach for gaining insights into local and global stone pathogenesis

Abstract

Background: In South Africa, kidney stones are relatively rare in the black population (B) compared to their white compatriots (W). Inter-race studies of urinary stone-risk factors have not identified unequivocal reasons to explain this anomaly.
Aim: The present hypotheses are that differences in urine composition between B and W may help explain this phenomenon and may provide insights into this disease more generally.
Setting: Data analysis of research conducted at the University of Cape Town.
Methods: This is a retrospective study involving urinary data collected between 1999 and 2012. These were analysed for conventional urinary risk factors that were categorised as metabolic, environmental and physicochemical. Statistical comparisons were performed (inter-race, inter-gender and control vs stone former). A relative analogous model was adopted in which B and W were regarded as low- and high-stone-risk groups, respectively.
Results: One thousand and thirty-three cases were investigated. Inter-race differences between controls indicated lower stone risk in B. Lower supersaturation of the calcium phosphate salt brushite (Bru) in B was noted as being important because it was the only physicochemical risk factor showing a difference and because of its mooted role as an initiator of stone formation. Higher supersaturation of Bru in males was also noted. There were no statistically significant differences between B and W stone formers.
Conclusion: Some conventional risk factors for kidney stones have a weaker impact on stone formation in B than in W, possibly because of a different urinary milieu in each group.
Contribution: Urinary Bru might be a key factor in explaining the South African stone anomaly and for gaining insights into stone formation globally.