Influence of factor VIIa and phospholipids on coagulation in "acquired" hemophilia

Objective-This study was performed to evaluate the influences of phospholipids and recombinant factor VIIa (rFVIIa) on thrombin generation and clot formation in "acquired" hemophilia B. Methods and Results-A synthetic mixture corresponding to hemophilia A (SHA) and "acquired" hemophilia B blood (AHBB) manufactured in vitro by an anti-FIX antibody were used in this study. With 10 pmol/L tissue factor (TF), 10 nmol/L rFVIIa, and saturating phospholipid, established thrombin generation in SHA was similar to that observed in the presence of factor VIII and rFVIIa at physiological concentrations. At lower phospholipid concentrations, thrombin generation was delayed and reduced. With 5 pmol/L TF, contact pathway-inhibited AHBB clotted later than normal blood and showed reduced clot stability and thrombin generation. These parameters of effectiveness were increased by the addition of phospholipids to AHBB, which restored clot stability and increased thrombin generation. No correction of clot formation or thrombin generation was observed when rFVIIa and phospholipids were added to AHBB in the absence of TF. Conclusions-The influence of rFVIIa is dependent on TF, and phospholipids substantially increase the hemostatic (or thrombotic) potential of rFVIIa/TF.