title: Long-term urine biobanking: storage stability of clinical chemical parameters under moderate freezing conditions without use of preservatives.
abstract: OBJECTIVE
  To examine the long-term stability and validity of analyte concentrations of 21 clinical biochemistry parameters in 24-h urine samples stored for 12 or 15 yr at -22°C and preservative free.
  
  
  METHODS
  Healthy children's 24-h urine samples in which the respective analytes had been measured shortly after sample collection (baseline) were reanalyzed. Second measurement was performed after 12 yr (organic acids) and 15 yr (creatinine, urea, osmolality, iodine, nitrogen, anions, cations, acid-base parameters) with the same analytical methodology. Paired comparisons and correlations between the baseline and repeated measurements were done. Recovery rates were calculated.
  
  
  RESULTS
  More than half of the analytes (creatinine, urea, iodine, nitrogen, sodium, potassium, magnesium, calcium, ammonium, bicarbonate, citric & uric acid) showed measurement values after >10 yr of storage not significantly different from baseline. 15 of the 21 parameters were highly correlated (r=0.99) between baseline and second measurement. Poorest correlation was r=0.77 for oxalate. Recovery ranged from 73% (oxalate) to 105% (phosphate).
  
  
  CONCLUSIONS
  Our results suggest high long-term stability and measurement validity for numerous clinical chemistry parameters stored at -22°C without addition of any urine preservative. Prospective storage of urine aliquots at -22°C for periods even exceeding 10 yr, appears to be an acceptable and valid tool in epidemiological settings for later quantification of several urine analytes.
authors.affiliation: DONALD Study Centre at the Research Institute of Child Nutrition, Department of Nutritional Epidemiology, Institute of Nutrition and Food Science (IEL), University of Bonn, Dortmund, Germany. Electronic address: remer@uni-bonn.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Remer
authors.affiliation: DONALD Study Centre at the Research Institute of Child Nutrition, Department of Nutritional Epidemiology, Institute of Nutrition and Food Science (IEL), University of Bonn, Dortmund, Germany.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Montenegro-Bethancourt
authors.affiliation: DONALD Study Centre at the Research Institute of Child Nutrition, Department of Nutritional Epidemiology, Institute of Nutrition and Food Science (IEL), University of Bonn, Dortmund, Germany.
authors.forename: Lijie
authors.initials: L
authors.lastname: Shi
mesh_terms: D064751:Ammonium Compounds / Q000652:urine; D001639:Bicarbonates / Q000652:urine; D018070:Biological Specimen Banks; D002118:Calcium / Q000652:urine; D002624:Chemistry, Clinical / Q000379:methods; D002648:Child; D002675:Child, Preschool; D019343:Citric Acid / Q000652:urine; D003404:Creatinine / Q000652:urine; D005260:Female; D005615:Freezing; D006801:Humans; D007455:Iodine / Q000652:urine; D008274:Magnesium / Q000652:urine; D008297:Male; D009584:Nitrogen / Q000652:urine; D011188:Potassium / Q000652:urine; D011446:Prospective Studies; D015203:Reproducibility of Results; D012964:Sodium / Q000652:urine; D013997:Time Factors; D014508:Urea / Q000652:urine; D014527:Uric Acid / Q000652:urine; D014556:Urine / Q000737:chemistry*; D059349:Urine Specimen Collection / Q000379:methods*
chemical_list: D064751:Ammonium Compounds; D001639:Bicarbonates; D014527:Uric Acid; D019343:Citric Acid; D014508:Urea; D007455:Iodine; D012964:Sodium; D003404:Creatinine; D008274:Magnesium; D009584:Nitrogen; D011188:Potassium; D002118:Calcium
keywords: 24-Hour urine; Clinical chemistry analytes; Metabolite stability; Preservative-free urine collection; Urine biobank