Lithogenic risk factors in normal black volunteers, and black and white recurrent stone formers.

OBJECTIVE: To compare lithogenic risk factors in normal black volunteer men (BN), male black stone formers (BSF) and male white recurrent stone formers (WSF); in addition, the differential diagnoses in the stone formers were compared to determine if the causes of renal stones differed in the two groups.

SUBJECTS AND METHODS: The study included 22 BN, 22 consecutive BSF and 122 consecutive WSF seen over a 10-year period. Each subject was assessed by a thorough medical history, dietary analysis and a full serum and urinary biochemical evaluation.

RESULTS: Although the WSF were significantly more overweight (P<0.001) and obese (P<0.001) than the BSF, neither group had values significantly different from those of their respective normal populations. There was no significant difference in serum levels of Ca, phosphorus, ionised Ca, calcitriol and alkaline phosphatase in BSF and WSF, but levels of parathyroid hormone tended to be (P<0.1) and calcitriol was significantly higher in BSF than WSF (P<0.03). The BSF urinary excretion levels tended to be more like that of the WSF, with the following pattern present; BN<BSF<WSF, except for citrate, where BSF< BN<WSF. No dietary or metabolic abnormality was found in 9% of BSF and 5% of WSF. Pure dietary lithogenic risk factors were present in 9% of BSF and 21% of WSF. The prevalence of metabolic risk factors was similar in the two groups but the distribution differed. Renal hypercalciuria, absorptive hypercalciuria and mild metabolic hyperoxaluria were 2.5-3 times more prevalent in the WSF.

CONCLUSION: Although the urine of BSF tends to be more like that of WSF, the lithogenic risk factors present differed and were less severe. The increase in urinary calcium excretion, coupled with a lower citrate excretion, may be the most important reason for stone formation in the black population. An increased protein intake may also play a role. In this small group of BSF there was no family history of urolithiasis, supporting the view that there may be a more prominent genetic influence in WSF.