2.4. Thromboelastography

TEG is a viscoelastic assay that measures coagulation kinetics of whole blood or platelet‐rich plasma. Primary metrics include R time that reflects time to initial fibrin formation, maximal amplitude (MA) that reflects the contribution of fibrin and platelets to ultimate clot strength, alpha angle that reflects the rate of fibrin formation, and lysis (LY30) that reflects the degree of fibrinolysis 30 minutes after the MA is reached.

TEG was performed using the Haemoscope TEG 5000 Coagulation Analyzer (Haemoscope Corp., Niles, Illinois). The final assay volume in the TEG cup was 360 μL which included 20 μL of 0.2 M CaCl₂, 36 μL of either recombinant TF dilutions or CCTs suspended in PBS at a concentration 10⁶ cells/mL and 304 μL of citrated whole blood. CaCl₂ was added to the TEG cup first followed by recombinant TF dilutions or CCTs and blood was added last. The sample was mixed twice using a pipette before starting the assay. The final molarity of CaCl₂ was 0.01 M. The final concentration of CCTs was 10⁵ cells/mL, which is similar to clinical trials administering CCTs which use a concentration of 1 to 10 × 10⁶ cells/kg.⁷, ¹⁰ Control assays had an identical volume of PBS vehicle added to each sample. Each sample was run in duplicate, and values for TEG parameters were averaged. Each trauma patient and control sample were assayed with the four different CCTs and compared to their controls. TEG was performed within 6 hours of collection for trauma patients and within 2 hours of collection for healthy controls. These TEG data are separate from the rapid TEG performed in the hospital, presented in Table 2.