Effects of freezing on tissue factor activity in a thromboelastography assay

Background Human recombinant tissue factor (TF) can be used to activate viscoelastic coagulation assays. Although the package insert indicates that TF should not be frozen, published scientific data are not available. Ability to store frozen aliquots of TF would increase laboratory efficiency and decrease costs associated with performing TF-activated assays. Objective The objectives of this study were to determine the effects of freezing and storage time on TF's ability to activate commercially available quality control material in thromboelastography (TEG). Methods TF was diluted and frozen at −20°C and −70°C for 72 hours, one week, 2 weeks, 3 months, and 6 months, and used for TEG after thawing. TF activation of control material was also assessed after TF storage at room temperature for 0, 24, and 48 hours. Time to fibrin formation (R), rate of clot formation (K and angle α), and clot strength (MA) were measured, and ANOVA used to identify differences. Results There were no significant differences in mean α and MA regardless of storage time or temperature. Means for R were not significantly increased at any time point after storage at room temperature or −70°C, but significant increases in mean R were observed after storage at −20°C starting after one week and continuing up to 6 months. Conclusion TF can be stored at room temperature for at least 48 hours, stored at −20°C for 72 hours, and stored at −70°C for up to 6 months without significant loss of activity for TEG.