title: Spot urine analysis: acidification does not increase calcium recovery.
abstract: BACKGROUND
  We investigated the effects of acidification and storage on calcium recovery in spot urine samples.
  
  
  METHODS
  In a retrospective study, 43 spot urine samples from patients with metabolic bone disease, which had been previously analysed fresh for calcium and creatinine, were acidified and incubated for 2 h at room temperature and re-analysed. In a prospective study, fresh spot urine samples from 15 volunteers were split into two aliquots--one left unacidified and the other acidified with 6 mol/L HCl to pH < 2. Both aliquots were analysed immediately and after storage at 4 degrees C for 24 h.
  
  
  RESULTS
  In both studies, the calcium creatinine ratios obtained on acidified and non-acidified spot urine samples were not different, both when measured immediately as well as after storage at 4 degrees C for 24 h.
  
  
  CONCLUSIONS
  The acidification of spot urine samples would thus appear to be unnecessary for calcium/creatinine measurements in metabolic bone disease if they were undertaken within at least 24 h.
authors.affiliation: Department of Core Clinical Pathology and Biochemistry, Royal Perth Hospital, Western Australia, Australia.
authors.forename: William
authors.initials: W
authors.lastname: McConnell
authors.forename: Samuel D
authors.initials: SD
authors.lastname: Vasikaran
mesh_terms: D001851:Bone Diseases, Metabolic / Q000652:urine*; D002118:Calcium / Q000652:urine*; D003404:Creatinine / Q000652:urine; D015925:Cryopreservation / Q000379:methods; D006801:Humans; D006851:Hydrochloric Acid / Q000737:chemistry; D011237:Predictive Value of Tests; D011309:Preservation, Biological; D011446:Prospective Studies; D012016:Reference Values; D012189:Retrospective Studies; D013048:Specimen Handling
chemical_list: D003404:Creatinine; D006851:Hydrochloric Acid; D002118:Calcium