Raising the alarm: endotoxin contamination in lithium heparin tubes is a threat to cell-based assay reliability

In vitro cytokine release assays are essential tools in immunological research, yet their reliability can be influenced by various pre-analytical factors. This study was initiated to investigate the potential impact of lithium heparin whole blood collection tubes from different manufacturers on assay performance. The objective of this work is to urge the scientific community to consider whole blood collection tubes as a significant and often underestimated source of variability in cell-based assays. 210 whole blood samples from healthy donors were collected in plastic lithium heparin tubes sourced from 20 different suppliers worldwide. Testing revealed that 8 out of 20 of these tubes contained endotoxin levels >0.1 EU/mL, which triggered significant variability in cytokine responses (IFN-γ and IL-6) in cell-based assays. A dose-response curve using LPS from E. coli confirmed the impact of endotoxins on interferon-γ production.