title: Physicochemical metabolic characteristics for calcium oxalate stone formation in patients with gouty diathesis.
abstract: OBJECTIVE
  We determined why calcium oxalate stones instead of uric acid stones form in some patients with gouty diathesis.
  
  
  METHODS
  Gouty diathesis was diagnosed from absence of secondary causes of uric acid stones or low urinary pH, and reduced fractional excretion of urate with discriminant score of the relationship between urinary pH and fractional excretion of urate less than 80. From the stone registry 163 patients with gouty diathesis were identified, including 62 with uric acid stones (GD + UA) and 101 patients with calcium oxalate stones (GD + Ca). Metabolic data and 24-hour urinary chemistry study were compared between the 2 groups.
  
  
  RESULTS
  Compared with GD + UA, GD + Ca had significantly greater urinary calcium (196 +/- 96 mg per day vs 162 +/- 82 mg per day, p <0.05) and significantly lower urinary citrate (430 +/- 228 vs 519 +/- 288 mg per day, p <0.05), resulting in higher urinary saturation of calcium oxalate. Both groups had low urinary pH (less than 5.5) and high urinary undissociated uric acid (greater than 100 mg/dl). Urinary calcium post-oral calcium load was significantly higher in GD + Ca than in GD + UA (0.227 vs 0.168 mg/dl glomerular filtrate, p <0.001).
  
  
  CONCLUSIONS
  Calcium oxalate stones may form in some patients with gouty diathesis due to increased urinary excretion of calcium and reduced excretion of citrate. Relative hypercalciuria in GD + Ca may be due to intestinal hyperabsorption of calcium.
authors.affiliation: Center for Mineral Metabolism and Clinical Research, The University of Texas Southwestern Medical Center, Dallas, Texas 75390-8885, USA. charles.pak@utsouthwestern.edu
authors.forename: Charles Y C
authors.initials: CY
authors.lastname: Pak
authors.forename: Orson W
authors.initials: OW
authors.lastname: Moe
authors.forename: Khashayar
authors.initials: K
authors.lastname: Sakhaee
authors.forename: Roy D
authors.initials: RD
authors.lastname: Peterson
authors.forename: John R
authors.initials: JR
authors.lastname: Poindexter
mesh_terms: D000328:Adult; D000368:Aged; D002129:Calcium Oxalate / Q000378:metabolism*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004198:Disease Susceptibility; D005260:Female; D006073:Gout / Q000150:complications* / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D014527:Uric Acid / Q000378:metabolism*; D014545:Urinary Calculi / Q000209:etiology* / Q000652:urine
chemical_list: D002129:Calcium Oxalate; D014527:Uric Acid