title: Effect of storage time at -20°C on markers used for assessment of renal damage in children: albumin, γ-glutamyl transpeptidase, N-acetyl-β-D-glucosaminidase and α1-microglobulin.
abstract: OBJECTIVE
  The objective of this study is to examine the influence of storage time at -20°C on the concentration of albumin, γ-glutamyl transpeptidase (γ-GT), N-acetyl-β-D-glucosaminidase (NAG), α(1)-microglobulin (A1M) and creatinine in a large sample of healthy children.
  
  
  METHODS
  The New England Children's Amalgam Trial followed 534 children, aged 6-10 at baseline, for 5 years, with annual urine collections. Urine samples were analysed for creatinine, albumin, γ-GT, NAG and A1M concentrations. Repeated measures analysis of covariance was used to model the effect of storage time on these concentrations.
  
  
  RESULTS
  The γ-GT concentration decreased significantly with storage time at -20°C. There was also a limited decrease in NAG. Albumin, A1M and creatinine concentrations did not appear to be affected by storage time at -20°C.
  
  
  CONCLUSIONS
  If it is necessary to interpret results from samples stored for a long time at -20°C, it is advisable to account for storage time in statistical models.
authors.affiliation: New England Research Institutes, Watertown, MA 02472, USA. ftrachtenberg@neriscience.com
authors.forename: Felicia
authors.initials: F
authors.lastname: Trachtenberg
authors.forename: Lars
authors.initials: L
authors.lastname: Barregard
mesh_terms: D000118:Acetylglucosaminidase / Q000652:urine*; D000419:Albuminuria / Q000652:urine; D000510:Alpha-Globulins / Q000652:urine; D015415:Biomarkers / Q000652:urine*; D002648:Child; D003404:Creatinine / Q000652:urine; D005260:Female; D006801:Humans; D007674:Kidney Diseases / Q000652:urine*; D008297:Male; D012034:Refrigeration; D013997:Time Factors; D005723:gamma-Glutamyltransferase / Q000652:urine*
chemical_list: D000510:Alpha-Globulins; D015415:Biomarkers; C016001:alpha-1-microglobulin; D003404:Creatinine; D005723:gamma-Glutamyltransferase; D000118:Acetylglucosaminidase