Impact of clinical sample handling and processing on ultra-low level measurements of plasma cytokines

Objectives: In this study, we evaluated the impact of clinical sample handling and processing on IL-6, IL-10, IFN gamma, and IL-2 measurements in plasma. Design and methods: We collected whole blood samples and analyzed various pre-analytical parameters. We assessed the following: 1) cytokine stability in whole blood that was stored over a ten-hour period at room temperature and 4 degrees C; 2) cytokine stability in plasma over 6 h; 3) vigorous sample handling including repeated dropping and transport through a pneumatic transport system; and 4) freeze-thaw stability of cytokines in plasma. To ensure ability to measure IL-6, IL-10, IFN gamma, and IL-2 levels in plasma, we used Simoa, an ultra-sensitive immunoassay platform. Results: We show that whole blood storage at room temperature results in decreased cytokine levels and that whole blood storage at 4 degrees C results in greater cytokine stability. We also show that cytokines are stable when whole blood samples are subjected to vigorous sample handling. Lastly, we show that cytokines are stable in plasma over three freeze-thaw cycles. Conclusions: Clinical sample handling and processing can affect measurements of IL-6, IL-10, IFN gamma, and IL-2 in plasma. We believe this study will be a useful reference for future studies in which these cytokines are used as potential biomarkers.