title: Influence of urine pH and citrate concentration on the upper limit of metastability for calcium phosphate.
abstract: OBJECTIVE
  We determined the effects on the urine upper limit of metastability for calcium phosphate of citrate concentration and pH, and achievement of the upper limit of metastability by adding calcium or phosphate.
  
  
  METHODS
  The citrate concentration in aliquots of 24-hour urine samples from normal males without a history of kidney stones was increased. The upper limit of metastability was determined by the point of visible crystal formation, as confirmed by increased optical density at 620 nm. when calcium or pH was increased. In additional experiments the upper limit of metastability was determined by adding calcium or phosphate at pH 5.9 and 6.4.
  
  
  RESULTS
  Regardless of how the upper limit of metastability was achieved increasing the citrate concentration increased the former value by about 0.4 units per mM. citrate per l. The upper limit of metastability achieved in a given urine sample by adding phosphate or calcium did not differ. Increasing urine pH increased the upper limit of metastability.
  
  
  CONCLUSIONS
  Treatment with alkaline citrate salts may decrease stone formation via an increase in calcium phosphate upper limit of metastability by increasing urine citrate and by directly affecting increased pH.
authors.affiliation: Renal Program, University of Chicago, Illinois, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Greischar
authors.forename: Y
authors.initials: Y
authors.lastname: Nakagawa
authors.forename: Frederic L
authors.initials: FL
authors.lastname: Coe
mesh_terms: D002118:Calcium / Q000652:urine; D002130:Calcium Phosphates / Q000652:urine*; D019343:Citric Acid / Q000652:urine*; D003460:Crystallization; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007669:Kidney Calculi / Q000652:urine; D008297:Male
chemical_list: D002130:Calcium Phosphates; D019343:Citric Acid; D002118:Calcium