AACR 2020 | Torq System Improves Liquid Biopsy Sample Shipping Stability

Ali Rahimian, Kyungjin Hong, Clara Neal, Gabriella Iacovetti, Greg Sommer, Ulrich Schaff

Sandstone Diagnostics, Pleasanton CA

Abstract

Quantifying circulating tumor DNA (ctDNA) markers for liquid biopsy testing often requires shipping blood samples to centralized laboratories. Mechanical damage to blood cells can occur during transport, especially if samples endure extensive vibration and temperature excursions. Such mechanical damage may result in Red Blood Cell (RBC) disruption known as in vitro hemolysis, as well as White Blood Cell (WBC) lysis leading to the release of nuclear DNA and several types of nucleases into the plasma. Nuclear DNA and nuclease contamination are the primary interfering factors impeding ctDNA recovery. Several commercial products are developed to address this issue by chemically stabilizing the cells in the tube during transport (e.g., the Streck cell-free DNA BCT™). Nevertheless, such products do not entirely resolve the problem, and cell lysis during shipping remains a complication. The Torq™ zero delay centrifuge system offers a novel solution by immediately centrifuging and separating plasma from the cell component at the point of collection, after the blood draw and prior to shipping, preventing ctDNA dilution from whole blood interferents. Here we compare hemolysis levels in blood samples collected and prepared by the Torq system and Streck BCTs following simulated shipping conditions including time, vibration, and temperature excursions.

Blood samples from healthy individuals were collected into Torq ZDiscs™ and Streck BCTs. The plasma was immediately separated within the ZDiscs using the Torq ZDrive™ and transferred to microtubes. The specimens in Streck BCTs remained as whole blood, as per the manufacturer’s instructions. Both sample types went through shipping simulation for 24 and 72 hours following ISTA 3A standards while experiencing temperature conditions of 4°C, 24°C, and 40°C. The blood within Streck BCTs was separated into plasma and cell components after reaching the designated time point, and all samples were inspected for hemolysis by quantifying hemoglobin content.

Samples collected and processed with the Torq zero delay centrifuge system showed minimal hemolysis throughout the simulation and at all temperature conditions, whereas samples in the Streck BCTs exhibited significantly higher hemolysis, especially after 72 hours (p-value: 0.0001). Streck samples stored at 4°C and 40°C were notably susceptible to high hemolysis contamination.

Compared to the Torq system, the Streck BCTs yielded significantly increased sample hemolysis following simulated shipping times and temperature excursions (both low and high), thereby increasing the likelihood of genomic contamination. The ZDiscs provide enhanced shipping resiliency and decreased nuclear DNA background, thus increasing the chance for rare mutation detection in liquid biopsy applications.