Effects of low and high factor X concentrations on thrombin generation in vitro

Introduction

Plasma factor X (FX) levels may affect the therapeutic effects of bypass hemostatic therapy among patients with hemophilia with inhibitors. This study aimed to reproduce low and high FX level conditions in vitro and analyze changes in coagulation capacity.

Materials and methods

To achieve low FX concentrations, FX-deficient plasma was preincubated with anti-factor VIII (FVIII) or anti-factor IX (FIX) antibody. Following this, it was incubated with activated factor VII (FVIIa) or FVIIa/FX mixture in the presence of FX (0.13–0.64 IU/mL). To achieve high FX concentrations, FVIII- or FIX-deficient plasma was preincubated with anti-FVIII or anti-FIX antibody. Next, FX (4–20 IU/mL) was added in the presence of FVIIa (140 IU/mL). Under both conditions, changes in coagulation capacity were assessed by evaluating thrombin generation (TG) and activated partial thromboplastin time (aPTT).

Results

FX at low concentrations induced concentration-dependent changes in TG. In the presence of FX (0.13 IU/mL), adding FVIIa inadequately restored TG. Further, TG in the plasma was normalized after adding FVIIa/FX (62.5/2 IU/mL), and the FVIIa/FX-added group had a stable TG and aPTT, regardless of FX concentrations (0.13–0.64 IU/mL). The FVIIa-added group exhibited a FX concentration-dependent increase in TG and a decrease in aPTT. Furthermore, TG increased with FX concentrations under high FX concentrations (up to 10 IU/mL).

Conclusions

Simultaneous FX supplementation in addition to FVIIa may be effective in promoting hemostasis under low plasma FX levels. Moreover, the risk of overcoagulation might be low even under high plasma FX levels.