title: Are stone analysis results different with repeated sampling?
abstract: BACKGROUND
  We assessed differences in results of stone analyses on subsequent sampling.
  
  
  METHODS
  A retrospective review of patients with stone analyses at a tertiary stone centre between March 2006 and July 2012 was performed. All stones were analyzed at a centralized laboratory using infrared spectroscopy. Patients were grouped according to the first predominant stone type on record, as defined by the predominant stone component of at least 60%. Stone groups included calcium oxalate (CaOx), calcium phosphate (CaP), uric acid (UA), cystine, struvite, mixed CaOx-CaP and mixed CaOx-UA. All patients had a full metabolic stone workup.
  
  
  RESULTS
  Of the 303 patients with stone analyses, 118 (38.9%) patients had multiple stone analyses. The mean age was 53.4 ± 15.1 years, and 87 (73.7%) were males. Of the 118, the initial stone analysis showed 43 CaOx, 38 CaP, 21 UA, 4 CaOx-CaP, 2 CaOx-UA, 6 cystine, and 4 struvite. There was a different stone composition in 25 (21.2%) patients with a median time delay of 64.5 days. Different compositions were found in 7 CaOx (to 3 CaP, 2 CaOx-CaP, and 2 UA), 5 CaP (to 3 CaOx and 2 CaOx-CaP), 3 UA (to 3 CaOx), 4 CaOx-CaP (to 2CaOx, 1 UA and 1 CaP), 2 CaOx-UA (to 2 CaOx) and 4 struvite (to 3 CaP and 1 UA).
  
  
  CONCLUSIONS
  Stone composition was different in 21.2% of patients on subsequent analyses.
authors.affiliation: Division of Urology, Department of Surgery, McGill University Health Centre, Montreal, QC.
authors.forename: Terence T N
authors.initials: TT
authors.lastname: Lee
authors.affiliation: Division of Urology, Department of Surgery, McGill University Health Centre, Montreal, QC.
authors.forename: Mohamed A
authors.initials: MA
authors.lastname: Elkoushy
authors.affiliation: Division of Urology, Department of Surgery, McGill University Health Centre, Montreal, QC.
authors.forename: Sero
authors.initials: S
authors.lastname: Andonian