title: Effect of repeated freeze-thaw cycles on urinary albumin-to-creatinine ratio.
abstract: BACKGROUND
  Urinary albumin-to-creatinine ratio (UACR) is widely used for diagnosis of chronic kidney disease in population investigation surveys. It is recommended that urinary albumin should be measured as soon as possible after urine is collected. It is not clear whether freezing and thawing affect the value of UACR and it is very inconvenient to measure UACR quickly in a population survey. The current study tries to determine the effect of repeated freezing and thawing on UACR to explore the possibility of freezing urine samples.
  
  
  METHODS
  Fifty-three urine samples with abnormal urinary albumin (ranging from 22.9 mg/L to 891.9 mg/L) were selected. The albumin and creatinine were measured before freezing, then all sample were stored at -30 degrees C. After being thawed at room temperature, the albumin and creatinine concentrations were measured again. The samples were frozen and thawed for five times, and albumin and creatinine were measured after each thawing. The measurements of albumin, creatinine, and UACR after each thawing were calculated and compared with its initial values using multiple comparisons of one-way ANOVA.
  
  
  RESULTS
  Compared with its initial value, urine albumin, creatinine and UACR all did not show any significant differences (p > 0.05).
  
  
  CONCLUSIONS
  It is feasible to freeze urine samples for future measurement of UACR. Urine samples can be safely frozen and thawed at least five times.
authors.affiliation: Institute of Nephrology, Peking University First Hospital, Beijing, China.
authors.forename: Yunfei
authors.initials: Y
authors.lastname: Bao
authors.forename: Li
authors.initials: L
authors.lastname: Zuo
mesh_terms: D000419:Albuminuria / Q000652:urine*; D000704:Analysis of Variance; D003404:Creatinine / Q000652:urine*; D005615:Freezing; D006801:Humans
chemical_list: D003404:Creatinine