Spatial fibrin clot formation is less affected by clotting factor deficiency than thrombin generation
E. Zöhrer, A. Schlagenhauf, S. Pohl, B. Leschnik, H. Haidl, S. Gallistl (Graz, Austria)
Time: 08:00 - 09:15
Objective: Thrombodynamics (TD) and Calibrated Automated Thrombography (CAT) are two methods frequently used in basic and translational research. Both assays differ from standard coagulation methods because they detect continuing enzymatic action after onset of clot formation, thus providing better insight into subtle changes of the haemostatic balance. In contrast to CAT, TD allows to differentiate between ‘initiation phase’ and ‘propagation phase’ as coagulation is activated by immobilized tissue factor (TF). This study aimed to assess the sensitivity of TD to deficiency of several clotting factors in comparison with CAT.
Methods: TD assays were performed with varying concentrations of (F) II, V, VII, VIII, IX, X and XI, using respective factor-deficient plasma samples in fractions of 0 to 100%. TD parameters (lag time, initial speed, average speed, clot size) were compared with CAT parameters [lag time, endogenous thrombin potential (ETP), peak, and time-to-peak (ttPeak)].
Results: Lag time, initial speed, average speed, and clot size determined by TD exhibited a reliable dependency on concentrations of all tested clotting factors. Although substantially reduced, clot development and propagation were still detected at 0% FVIII, FIX or FXI. Clot propagation declined exponentially at FII concentrations below 4% as well as at FV and FX concentrations below 1%. FVIII levels below 10% resulted in thrombin generation traces too low for evaluation (ETP not calculable), while TD parameters were less affected. TD parameters exhibited lower sensitivity but higher consistency than CAT parameters in detecting coagulation factor deficiencies.
Conclusion: The TD assay shows that reduced but persistent clot formation occurs even at complete deficiency of FVII, FVIII, FIX, or FXI. This can be explained by the compensatory effects of extrinsic and intrinsic components perpetuating clot formation even in conditions where thrombin generation is largely abrogated. Very small amounts of thrombin (>4%) were required to maintain stable clot propagation when tissue factor was immobilized on a surface. TD parameters reflect in vivo conditions of hemophiliacs exhibiting a significantly higher risk of bleeding at FVIII levels <5% better than CAT parameters due to higher sensitivity towards very low FVIII levels.