Long-term stability of biochemical markers in pediatric serum specimens stored at -80°C: A CALIPER Substudy

Objectives: Pediatric serum samples collected from healthy children in the CALIPER (Canadian Laboratory Initiative in Pediatric Reference Interval) project are stored at -80 degrees C for various periods of time. This study aimed to determine the stability of chemistry, protein, and hormone analytes under these conditions. Design and 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 degrees 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 (R) Chemistry System, COBAS INTEGRA (R) 400 Plus and IMMULITE (R) 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 degrees 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. (C) 2012 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.