title: Long-term stability of biochemical markers in pediatric serum specimens stored at -80 °C: a CALIPER Substudy.
abstract: OBJECTIVE
  Pediatric serum samples collected from healthy children in the CALIPER (Canadian Laboratory Initiative in Pediatric Reference Interval) project are stored at -80 °C for various periods of time. This study aimed to determine the stability of chemistry, protein, and hormone analytes under these conditions.
  
  
  METHODS
  Serum samples collected from children of 0-18 years of age attending outpatient clinics were pooled into a single pool or into age-group specific pools. Following baseline measurement, each pool was aliquoted and kept frozen at -80 °C until analysis. Samples were analyzed for 57 biochemical markers at monthly intervals over a 10-13 month period and each aliquot was subject to one freeze-thaw cycle before analysis. The analysis was performed on VITROS Chemistry System, COBAS INTEGRA 400 Plus and IMMULITE 2500. Values obtained at monthly intervals were compared to baseline measurements and examined for trends over time.
  
  
  RESULTS
  A majority of analytes measured in this study showed no significant time-dependent change relative to baseline or trend over time after up to 13 months of storage. PTH showed up to 27.2% decline after 10 months of storage with most of the decline evident after 2 months. Most analytes showed variability over time, which is thought to reflect assay variability rather than changes in analyte stability.
  
  
  CONCLUSIONS
  The study shows stability for a majority of analytes stored in serum at -80 °C after up to 13 months of storage. Samples do not require immediate testing for reference interval determination for the selected analytes with possible exception of PTH.
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Davor
authors.initials: D
authors.lastname: Brinc
authors.forename: Man Khun
authors.initials: MK
authors.lastname: Chan
authors.forename: Allison A
authors.initials: AA
authors.lastname: Venner
authors.forename: Maria D
authors.initials: MD
authors.lastname: Pasic
authors.forename: David
authors.initials: D
authors.lastname: Colantonio
authors.forename: Lianna
authors.initials: L
authors.lastname: Kyriakopolou
authors.forename: Khosrow
authors.initials: K
authors.lastname: Adeli
mesh_terms: D000293:Adolescent; D015415:Biomarkers / Q000097:blood*; D001774:Blood Chemical Analysis / Q000295:instrumentation / Q000379:methods; D001793:Blood Preservation / Q000379:methods*; D002170:Canada; D002648:Child; D002675:Child, Preschool; D019411:Clinical Laboratory Techniques / Q000295:instrumentation / Q000379:methods; D015925:Cryopreservation / Q000379:methods*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D015203:Reproducibility of Results; D013997:Time Factors
chemical_list: D015415:Biomarkers