title: Collection and storage of urine specimens for measurement of urolithiasis risk factors.
abstract: OBJECTIVE
  To evaluate how different methods for storage and preservation of urine samples affected the outcome of analysis of risk factors for stone formation.
  
  
  METHODS
  Spot urine samples were collected from 21 healthy volunteers. Each fresh urine sample was divided into ten 10-mL aliquots: 2 without preservative, 2 with thymol, 2 with toluene, 2 with hydrochloric acid (HCl), and 2 with sodium azide. One sample of each pair was stored at 4 °C and the other at room temperature. The concentrations of calcium, magnesium, sodium, phosphate, urate, oxalate, citrate, and pH in each urine sample were analyzed immediately after collection (0 hour) and after 24 and 48 hours.
  
  
  RESULTS
  There were no significant differences in calcium, oxalate, magnesium, phosphate, sodium, urate or pH (without acidification) between samples with different preservation methods (P >.05). Urinary citrate, however, was significantly lower in the urine collected with HCl than when other preservatives were used, both at room temperature and at 4 °C. Urine pH was significantly higher after 48 hours than after 24 hours, whether the samples were stored at room temperature or at 4 °C.
  
  
  CONCLUSIONS
  Antibacterial preservatives (eg, thymol or toluene) can be recommended as preservatives for 24-hour urine collections. Ideally, the samples should be stored at 4 °C. When HCl is used as a preservative, it seems essential to neutralize the samples before analysis. This is particularly obvious with the chromatographic method used for analysis of citrate that was used in this study.
authors.affiliation: Department of Urology, Minimally Invasive Surgery Center, the First Affiliated Hospital of Guangzhou Medical University, Guangdong Key Laboratory of Urology, Guangzhou, China. Electronic address: wwqwml@163.com.
authors.forename: Wenqi
authors.initials: W
authors.lastname: Wu
authors.affiliation: Department of Urology, Minimally Invasive Surgery Center, the First Affiliated Hospital of Guangzhou Medical University, Guangdong Key Laboratory of Urology, Guangzhou, China.
authors.forename: Dong
authors.initials: D
authors.lastname: Yang
authors.affiliation: Division of Urology, Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Hans-Goran
authors.initials: HG
authors.lastname: Tiselius
authors.affiliation: Department of Urology, Minimally Invasive Surgery Center, the First Affiliated Hospital of Guangzhou Medical University, Guangdong Key Laboratory of Urology, Guangzhou, China.
authors.forename: Lili
authors.initials: L
authors.lastname: Ou
authors.affiliation: Department of Urology, Minimally Invasive Surgery Center, the First Affiliated Hospital of Guangzhou Medical University, Guangdong Key Laboratory of Urology, Guangzhou, China.
authors.forename: Zanlin
authors.initials: Z
authors.lastname: Mai
authors.affiliation: Department of Urology, Minimally Invasive Surgery Center, the First Affiliated Hospital of Guangzhou Medical University, Guangdong Key Laboratory of Urology, Guangzhou, China.
authors.forename: Kang
authors.initials: K
authors.lastname: Chen
authors.affiliation: Department of Urology, Minimally Invasive Surgery Center, the First Affiliated Hospital of Guangzhou Medical University, Guangdong Key Laboratory of Urology, Guangzhou, China.
authors.forename: Hanliang
authors.initials: H
authors.lastname: Zhu
authors.affiliation: Department of Urology, Minimally Invasive Surgery Center, the First Affiliated Hospital of Guangzhou Medical University, Guangdong Key Laboratory of Urology, Guangzhou, China.
authors.forename: Shaohong
authors.initials: S
authors.lastname: Xu
authors.affiliation: Department of Urology, Minimally Invasive Surgery Center, the First Affiliated Hospital of Guangzhou Medical University, Guangdong Key Laboratory of Urology, Guangzhou, China.
authors.forename: Zhijian
authors.initials: Z
authors.lastname: Zhao
authors.affiliation: Department of Urology, Minimally Invasive Surgery Center, the First Affiliated Hospital of Guangzhou Medical University, Guangdong Key Laboratory of Urology, Guangzhou, China.
authors.forename: Guohua
authors.initials: G
authors.lastname: Zeng
mesh_terms: D006801:Humans; D018570:Risk Assessment; D012307:Risk Factors; D013048:Specimen Handling / Q000379:methods*; D052878:Urolithiasis / Q000209:etiology / Q000652:urine*