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The stability of select biomarkers in frozen plasma over time: an evaluation of a low-volume sample analyzer

In medicine, and in medical research specifically, the levels of biomarkers in body fluids are often analyzed, as many of these are indicators of biological state or function and uniquely correlate with a specific human disease [1]. Given that many clinical studies will run for periods that exceed months or even years, the stability of samples and the degradation of important molecules is of primary concern for researchers. Short storage stability creates issues for experimental designs in which batch analysis is most efficient, for additional measurements at a later date, and for multisite studies in which samples must be shipped to the primary site. The frequency and size of the shipments, as well as the transit conditions, can make this process cumbersome and costly. In addition, storage of human clinical samples is subject to strict regulations with respect to recording and reporting. Thus, managing study costs and resources depends heavily on the ability to analyze samples in batches and to use a single location and common temperature that are appropriate for all future analyses. Accordingly, specifications that are incomplete with respect to storage temperatures, or that vary between analytes, are problematic. Past studies have investigated the degradation of biomarkers or analytes in either plasma or serum over varying periods and at various storage temperatures [2–6]. However, the variety of factors that cause differences in results from analyses involving serum vs. plasma (e.g., pseudohyperkalemia, post-centrifugal coagulation, cation interference [7]), combined with the costs and importance of human clinical studies, highlights the fact that these differences, along with inter-species variability, cannot be overlooked. In addition, there is a lack of information relating to ultra-cold storage stability in past studies and, as this type of storage is now widely available, new and updated specifications are required. In this study, we sought to examine the stability of various biomarkers in stored plasma at specific time points over a period of 1 year and to validate the results from our in-house low-volume analyzer by comparing its output to the results received from a clinical diagnostic services (DS) laboratory. Measurements were made with the Cobas c111, a low-volume analyzer from Roche Diagnostics (Indianapolis, IN, USA) designed for small workload laboratories. Ten apparently healthy subjects (5 men and 5 women) between the ages of 23 and 58 years (mean = 33 years) were recruited. Participants with a history of conditions affecting the liver, muscles, or kidneys or with acute infectious diseases were excluded. The experimental protocol was approved by the Research Ethics Board of the University of Manitoba and by the Research Review Committee of the St. Boniface Hospital. Analysis on the Cobas c111 autoanalyzer was done weekly or bi-weekly for the first 8 weeks (weeks 1, 2, 3, 4, 6, and 8) and monthly for the rest of year 1 (months 3 through 12). All Cobas reagents were calibrated on a lotto-lot basis with appropriate company calibrators and tested with either 2or 6-point controls [high-sensitivity *Corresponding author: Peter Zahradka, Canadian Centre for Agri-Food Research in Health and Medicine, St. Boniface Hospital Research Centre, 351 Tache Avenue, Winnipeg, MB, Canada R2H 2A6, Phone: +1-204-235-3507, Fax: +1-204-237-4018, E-mail: peterz@sbrc.ca; Department of Physiology, University of Manitoba, Winnipeg, MB, Canada; and Department of Human Nutritional Sciences, University of Manitoba, Winnipeg, MB, Canada Raissa Perrault: Canadian Centre for Agri-Food Research in Health and Medicine, St. Boniface Hospital Research Centre, Winnipeg, MB, Canada; and Department of Physiology, University of Manitoba, Winnipeg, MB, Canada Carla G. Taylor: Canadian Centre for Agri-Food Research in Health and Medicine, St. Boniface Hospital Research Centre, Winnipeg, MB, Canada; Department of Physiology, University of Manitoba, Winnipeg, MB, Canada; and Department of Human Nutritional Sciences, University of Manitoba, Winnipeg, MB, Canada