title: Predicting Patients with Inadequate 24- or 48-Hour Urine Collections at Time of Metabolic Stone Evaluation.
abstract: OBJECTIVE
  We aimed to understand the characteristics of patients who are less likely to submit adequate urine collections at metabolic stone evaluation.
  
  
  METHODS
  Inadequate urine collection was defined using two definitions: (1) Reference ranges for 24-hour creatinine/kilogram (Cr/24) and (2) discrepancy in total 24-hour urine Cr between 24-hour urine collections. There were 1502 patients with ≥1 kidney stone between 1998 and 2014 who performed a 24- or 48-hour urine collection at Northwestern Memorial Hospital and who were identified retrospectively. Multivariate analysis was performed to analyze predictor variables for adequate urine collection.
  
  
  RESULTS
  A total of 2852 urine collections were analyzed. Mean age for males was 54.4 years (range 17-86), and for females was 50.2 years (range 8-90). One patient in the study was younger than 17 years old. (1) Analysis based on the Cr 24/kg definition: There were 50.7% of patients who supplied an inadequate sample. Females were nearly 50% less likely to supply an adequate sample compared with men, P<0.001. Diabetes (odds ratio [OR] 1.42 [1.04-1.94], P=0.026) and vitamin D supplementation (OR 0.64 [0.43-0.95], P=0.028) predicted receiving an adequate/inadequate sample, respectively. (2) Analysis based on differences between total urinary Cr: The model was stratified based on percentage differences between samples up to 50%. At 10%, 20%, 30%, 40%, and 50% differences, inadequate collections were achieved in 82.8%, 66.9%, 51.7%, 38.5%, and 26.4% of patients, respectively. Statistical significance was observed based on differences of ≥40%, and this was defined as the threshold for an inadequate sample. Female sex (OR 0.73 [0.54-0.98], P=0.037) predicted supplying inadequate samples. Adequate collections were more likely to be received on a Sunday (OR 1.6 [1.03-2.58], P=0.038) and by sedentary workers (OR 2.3 [1.12-4.72], P=0.023).
  
  
  CONCLUSIONS
  Urine collections from patients during metabolic evaluation for nephrolithiasis may be considered inadequate based on two commonly used clinical definitions. This may have therapeutic or economic ramifications and the propensity for females to supply inadequate samples should be investigated further.
authors.affiliation: Department of Urology, Northwestern University Feinberg School of Medicine , Chicago, Illinois.
authors.forename: Barry B
authors.initials: BB
authors.lastname: McGuire
authors.affiliation: Department of Urology, Northwestern University Feinberg School of Medicine , Chicago, Illinois.
authors.forename: Yasin
authors.initials: Y
authors.lastname: Bhanji
authors.affiliation: Department of Urology, Northwestern University Feinberg School of Medicine , Chicago, Illinois.
authors.forename: Vidit
authors.initials: V
authors.lastname: Sharma
authors.affiliation: Department of Urology, Northwestern University Feinberg School of Medicine , Chicago, Illinois.
authors.forename: Brendan T
authors.initials: BT
authors.lastname: Frainey
authors.affiliation: Department of Urology, Northwestern University Feinberg School of Medicine , Chicago, Illinois.
authors.forename: Megan
authors.initials: M
authors.lastname: McClean
authors.affiliation: Department of Urology, Northwestern University Feinberg School of Medicine , Chicago, Illinois.
authors.forename: Caroline
authors.initials: C
authors.lastname: Dong
authors.affiliation: Department of Urology, Northwestern University Feinberg School of Medicine , Chicago, Illinois.
authors.forename: Kalen
authors.initials: K
authors.lastname: Rimar
authors.affiliation: Department of Urology, Northwestern University Feinberg School of Medicine , Chicago, Illinois.
authors.forename: Kent T
authors.initials: KT
authors.lastname: Perry
authors.affiliation: Department of Urology, Northwestern University Feinberg School of Medicine , Chicago, Illinois.
authors.forename: Robert B
authors.initials: RB
authors.lastname: Nadler
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003404:Creatinine / Q000652:urine*; D005260:Female; D006801:Humans; D007087:Illinois; D007669:Kidney Calculi / Q000503:physiopathology* / Q000652:urine; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010349:Patient Compliance; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D013997:Time Factors; D059349:Urine Specimen Collection / Q000706:statistics & numerical data*; D055815:Young Adult
chemical_list: D003404:Creatinine