Introduction: Standardized pre-analytical blood sample procedures for the analysis of circulating cell-free DNA (ccfDNA) are still not available. Therefore, the present study aimed at evaluating the impact of storage conditions related to different times (24 and 48 h) and temperatures (room temperature (RT) and 4 - 8 °C) on the plasma ccfDNA concentration of blood samples drawn into Cell-Free DNA collection tubes (Roche Diagnostics GmbH, Mannheim, Germany).
Materials and methods: Venous blood from 30 healthy individuals was collected into five 8.5 mL Cell-Free DNA Collection Tubes (Roche Diagnostics GmbH) each. Plasma samples were processed at time point of blood collection (tube 1), and after storage under the following conditions: 24 h at RT (tube 2) or 4-8 °C (tube 3), and 48 h at RT (tube 4) or 4 - 8 °C (tube 5). Circulating cell-free DNA concentrations were determined by EvaGreen chemistry-based droplet digital PCR (ddPCR).
Results: No statistically significant differences between median (interquartile range) plasma ccfDNA concentrations (ng/mL) at time point of blood collection (3.17 (2.13 - 3.76)) and after storage for 24 h (RT: 3.02 (2.41 - 3.68); 4-8 °C: 3.21 (2.19 - 3.46)) and 48 h (RT: 3.13 (2.10 - 3.76); 4-8 °C: 3.09 (2.19 - 3.50)) were observed (P values from 0.102 - 0.975).
Conclusions: No unwanted release of genomic DNA from white blood cells could be detected in plasma samples after tube storage for 24 and 48 h regardless of storage temperature.
Keywords: cell-free nucleic acids; pre-analytical phase; quality improvement.