title: How Much Information is Lost When You Only Collect One 24-Hour Urine Sample during the Initial Metabolic Evaluation?
abstract: OBJECTIVE
  During the initial metabolic evaluation the need for 1 vs 2, 24-hour urine collections is debated. While data suggest that mean urine chemistry measures are similar on consecutive samples, it remains unclear how much, if any, information is lost when only 1 sample is collected.
  
  
  METHODS
  Using analytical files from Litholink Corporation® (1995 to 2013) we identified adults with kidney stones who underwent initial metabolic testing. Next we determined the subset of patients who collected 2, 24-hour urine samples with urine creatinine varying by 10% or less during a 7-day time window. We then examined the degree of variability in urine chemistry profiles. Specifically we calculated the mean absolute value of the difference between samples as well as the percent difference for individual urine parameters.
  
  
  RESULTS
  We identified 70,192 patients meeting our eligibility criteria. While the overall means for individual urine parameters did not vary between samples, the percent difference between the samples varied widely. For example, nearly 1 in 3 patients had a 30% or greater difference in urine calcium and volume between 2 consecutive samples. We noted that inconsistencies between samples often involved multiple parameters. For instance, 29% and 25% of patients had a 20% difference in 2 and 3 or more parameters, respectively.
  
  
  CONCLUSIONS
  We observed substantial differences between consecutive 24-hour urine samples that could affect clinical decision making. In light of these findings clinicians must weigh the information lost from only 1 collection vs the burden to the patient of collecting 2.
authors.affiliation: Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, Michigan; Department of Surgery, College of Medicine, Al-Imam Muhammad Ibn Saud Islamic University (IMSIU), Riyadh, Saudi Arabia.
authors.forename: Abdulrahman F
authors.initials: AF
authors.lastname: Alruwaily
authors.affiliation: Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, Michigan.
authors.forename: Casey A
authors.initials: CA
authors.lastname: Dauw
authors.affiliation: Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, Michigan.
authors.forename: Maggie J
authors.initials: MJ
authors.lastname: Bierlein
authors.affiliation: Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, Michigan.
authors.forename: Phyllis
authors.initials: P
authors.lastname: Yan
authors.affiliation: Litholink Corporation, Laboratory Corporation of America Holdings, Chicago, Illinois.
authors.forename: John R
authors.initials: JR
authors.lastname: Asplin
authors.affiliation: Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, Michigan.
authors.forename: Khurshid R
authors.initials: KR
authors.lastname: Ghani
authors.affiliation: Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, Michigan.
authors.forename: J Stuart
authors.initials: JS
authors.lastname: Wolf
authors.affiliation: Divisions of Endourology and Health Services Research, Department of Urology, University of Michigan, Ann Arbor, Michigan. Electronic address: kinks@med.umich.edu.
authors.forename: John M
authors.initials: JM
authors.lastname: Hollingsworth
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003404:Creatinine / Q000652:urine*; D003625:Data Collection / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007669:Kidney Calculi / Q000652:urine*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D016482:Urinalysis; D059349:Urine Specimen Collection / Q000379:methods / Q000706:statistics & numerical data*; D055815:Young Adult
chemical_list: D003404:Creatinine
keywords: nephrolithiasis; quality of health care; secondary prevention; urinalysis