title: Adequate or not? A comparison of 24-hour urine studies for renal stone prevention by creatinine to weight ratio.
abstract: OBJECTIVE
  The intent of this study was to compare urine parameters between kidney stone formers with low, expected, and high creatinine to weight ratio (Cr/kg) and to discuss implications for treatment.
  
  
  METHODS
  In this retrospective study, 381 stone formers (205 females and 176 males) with urine collections for nephrolithiasis evaluation were included. Using the first collected sample, patients were grouped into low, expected, and high Cr/kg using sex appropriate reference ranges (15.0-20.0 mg/kg for females and 18.0-24.0 mg/kg for males) and evaluated.
  
  
  RESULTS
  Of initial collections, 50.7% were outside the Cr/kg reference range. Median age increased as Cr/kg decreased with 13 years age difference between low (56) and high (43) groups. Body mass index and weight also increased significantly with decreased ratio. No significant difference between groups was found for urine volume, total oxalate, oxalate concentration, pH, and supersaturations of calcium oxalate and uric acid. Total calcium, sodium, citrate, calcium concentration, supersaturation of calcium phosphate, and other parameters significantly increased with increased Cr/kg for the cohort.
  
  
  CONCLUSIONS
  To our knowledge, this is the first study to thoroughly evaluate the impact of Cr/kg on urine parameters. Clinicians should be cognizant of limitations of Cr/kg for evaluating collection adequacy. It is especially important to consider Cr/kg when there is potential for undertreatment or overtreatment of patients with abnormal Cr/kg. Studies demonstrating hypercalciuria and high Cr/kg may need to be repeated before starting thiazide diuretics. Further studies are needed to determine how to better interpret urine components that vary with Cr/kg ratio.
authors.affiliation: Department of Urologic Surgery, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Sawyer
authors.forename: Mary S
authors.initials: MS
authors.lastname: Dietrich
authors.forename: Ryan B
authors.initials: RB
authors.lastname: Pickens
authors.forename: S Duke
authors.initials: SD
authors.lastname: Herrell
authors.forename: Nicole L
authors.initials: NL
authors.lastname: Miller
mesh_terms: D000328:Adult; D002118:Calcium / Q000652:urine; D015331:Cohort Studies; D003404:Creatinine / Q000652:urine*; D005260:Female; D006801:Humans; D007669:Kidney Calculi / Q000473:pathology* / Q000652:urine*; D008297:Male; D008875:Middle Aged; D009929:Organ Size
chemical_list: D003404:Creatinine; D002118:Calcium