title: Lithogenic risk factors in the urine of black and white subjects.
abstract: OBJECTIVE
  To identify biochemical and dietary factors which may play a role in the low incidence of stone formation in the black South African population.
  
  
  METHODS
  The study included 31 semiurbanized black and 29 urbanized white subjects. The protocol and modern laboratory techniques used to assess recurrent stone formers were followed. Urinary sodium, potassium, creatinine, calcium, phosphate and urate levels were measured, and urinary citrate, 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 significantly higher (P < 0.001) in black than in white subjects. Urinary potassium, calcium, citrate, phosphate and cystine were all significantly lower in black than in white subjects (P < 0.001 for the first four and P < 0.03 for cystine).
  
  
  CONCLUSIONS
  Certain intrinsic factors in South African black subjects may account for their lower frequency of stone formation than in white subjects. Of these, the very low urinary calcium, decreased urinary cystine and different interactions between sodium and calcium/cystine are probably important.
authors.affiliation: Department of Medicine, Johannesburg Hospital, South Africa.
authors.forename: N A
authors.initials: NA
authors.lastname: Whalley
authors.forename: M F
authors.initials: MF
authors.lastname: Moraes
authors.forename: T G
authors.initials: TG
authors.lastname: Shar
authors.forename: S S
authors.initials: SS
authors.lastname: Pretorius
authors.forename: A M
authors.initials: AM
authors.lastname: Meyers
mesh_terms: D000328:Adult; D044383:Black People; D002136:Calcium, Dietary / Q000008:administration & dosage; D019343:Citric Acid / Q000652:urine; D004032:Diet / Q000009:adverse effects*; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D010070:Oxalates / Q000008:administration & dosage / Q000652:urine; D010710:Phosphates / Q000652:urine; D011188:Potassium / Q000652:urine; D012307:Risk Factors; D012964:Sodium / Q000652:urine; D013019:South Africa / Q000453:epidemiology; D014545:Urinary Calculi / Q000208:ethnology / Q000209:etiology / Q000652:urine*; D044465:White People
chemical_list: D002136:Calcium, Dietary; D010070:Oxalates; D010710:Phosphates; D019343:Citric Acid; D012964:Sodium; D011188:Potassium