title: A single 24-hour urine collection is inadequate for the medical evaluation of nephrolithiasis.
abstract: OBJECTIVE
  We determined the adequacy of a single 24-hour urine sample for evaluating patients for medical renal stone prevention.
  
  
  METHODS
  A total of 459 patients from a private urology practice specializing in the treatment of urolithiasis and 683 from a university stone research clinic provided 2 and 3, 24-hour urine samples, respectively. We used samples 1 and 2 from private practice patients, and 1 and 3 from university clinic patients for analysis, and compared each to the others by correlation coefficients and calculation of the mean difference plus or minus standard deviation (SD) of the difference. Urine risk factors were measured by standard methods.
  
  
  RESULTS
  Although the correlation of urine values 1 and 2 was excellent for all stone risk factors, SD values for the differences were large enough that within 1 SD on either side of 0, which included 68.8% of cases, by chance urine 1 would depart from urine 2 by clinically important amounts. These departures would be more than sufficient to misdiagnose common metabolic disorders.
  
  
  CONCLUSIONS
  A single 24-hour sample is not sufficient for evaluating patients before metabolic treatment for stone prevention because misdiagnosis is common, leading to inappropriate treatment.
authors.affiliation: Nephrology Section, University of Chicago and LithoLink Corp., Chicago, Illinois, USA.
authors.forename: Joan H
authors.initials: JH
authors.lastname: Parks
authors.forename: Evan
authors.initials: E
authors.lastname: Goldfisher
authors.forename: John R
authors.initials: JR
authors.lastname: Asplin
authors.forename: Fredric L
authors.initials: FL
authors.lastname: Coe
mesh_terms: D005260:Female; D006801:Humans; D007669:Kidney Calculi / Q000175:diagnosis*; D008297:Male; D013048:Specimen Handling; D013997:Time Factors; D014556:Urine