Limited factor VII a surface localization requirement of the factor VII a–induced overall thrombin generation in platelet‐rich hemophilia A plasma

Background Thrombin generation assay ( TGA ) and thrombelastography ( TEG ) are increasingly employed, global, in vitro methods for assessment of the procoagulant potential of plasma/blood and possibly ideally suited tools to monitor, for example, therapy with recombinant factor VII a ( FVII a). It remains controversial to what extent results obtained with spiked and postinfusion samples reflect the outcome in patients. Objective To characterize the TGA response to FVII a in hemophilic plasma and compare with TEG data. Methods Hemophilia A ( HA ) was induced in platelet‐rich plasma ( PRP ) from healthy volunteers, followed by spiking with FVII a, γ‐carboxyglutamic acid (Gla)‐domainless FVII a or V158D/E296V/M298Q‐ FVII a ( FVII a DVQ ). Samples were triggered with tissue factor and analyzed by TGA and TEG in parallel. Results Addition of 25 nmol L −1 FVII a to HA PRP normalized TEG parameters angle and R time, as well as TGA lag time, but had poor effects on the thrombin peak height and velocity index. All parameters (at least) returned to normal levels either upon adding a much higher concentration of FVII a (~1500 nmol L −1 ) or by using the superactive variant FVII a DVQ . Surprisingly, Gla‐domainless derivatives of FVII a and FVII a DVQ also yielded considerable effects in HA PRP . Conclusions The good general responses to clinically effective concentrations of FVII a (25 and 75 nmol L −1 ) seen in TEG analyses, as well as for TGA lag time, were accompanied by far‐from‐normal thrombin peaks. A near‐normal thrombin peak response required the presence of considerably higher FVII a activity but, intriguingly, relied only marginally on a functional Gla domain (ie, on platelet surface localization).