title: Adequacy of a single 24-hour urine collection for metabolic evaluation of recurrent nephrolithiasis.
abstract: OBJECTIVE
  There is much debate about whether 1 or 2, 24-hour urinalyses are adequate for metabolic evaluation of stone formers. We determined whether repeat 24-hour urine collection provides information similar to that of the initial 24-hour urine collection and whether repeat collection is necessary.
  
  
  METHODS
  We analyzed 2, 24-hour urine collections in 777 patients obtained from 2001 to 2005. Samples were collected 3 days or less apart before pharmacological intervention and analyzed elsewhere for routine stone risk profiles of urine calcium, oxalate, citrate, uric acid, sodium, potassium, magnesium, phosphorus, ammonium, chloride, urea nitrogen and creatinine.
  
  
  RESULTS
  No parameters showed a statistically significant difference between 24-hour urine samples 1 and 2 when mean values were compared (pairwise t test each p >0.05, range 0.06 to 0.87). Using Pearson's correlation all parameters showed positive correlation coefficients (r = 0.68 to 0.89, each p <0.0001). The mean of individual patient differences in samples 1 and 2 were compared to 0 and 6 of 12 showed no difference (p >0.05) while for the remaining 6 p value was <0.05. The percent difference was 0.5% to 4.19% for all urinary parameters.
  
  
  CONCLUSIONS
  One 24-hour urine sample is sufficient for metabolic evaluation of recurrent stone disease. There is no significant difference in 12 urinary parameters between 24-hour urine samples collected within 3 days of each other. This information is useful to providers and may decrease patient inconvenience and the overall cost of metabolic stone evaluation.
authors.affiliation: Department of Urology, University of California-San Francisco, San Francisco, California, USA.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Castle
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Cooperberg
authors.forename: Natalia
authors.initials: N
authors.lastname: Sadetsky
authors.forename: Brian H
authors.initials: BH
authors.lastname: Eisner
authors.forename: Marshall L
authors.initials: ML
authors.lastname: Stoller
mesh_terms: D002940:Circadian Rhythm; D006801:Humans; D053040:Nephrolithiasis / Q000378:metabolism / Q000652:urine*; D012008:Recurrence; D012189:Retrospective Studies