PB0067 - Monitoring the anticoagulation level of warfarin with a new VII-prothrombin time

Background: Prothrombin time (PT) is the primary laboratory test used to monitor the anticoagulation ability of warfarin. Coagulation factor VII can be inhibited by warfarin and monitored by PT but has little contribution to thrombin generation. As factor VII has the shortest half-life among factor II/VII/IX/X, it is the main contributor of PT prolongation at the induction phase of warfarin treatment. Studies have shown that the classic PT test is not suitable for warfarin monitoring at the induction phase. By adding factor VII rich plasma, a newly amended method (Fiix-PT) affected by Factor II/X without disturbance of factor VII is a potential substitution of PT.

Aims: In response to the disadvantage of plasma reagent it was decided to construct a new VII-PT method by applying recombinant factor VII instead of factor VII rich plasma to monitor warfarin therapy.

Methods: A sufficient amount of recombinant factor VII was added into the PT reagent (Stago, France) to construct VII-PT assay and the VII-PT specific ISI was determined. VII-PT sensitivity to factor II/VII/X was evaluated. PT-INR, VII-PT-INR and factor II/VII/X were determined in patients taking warfarin during the first month.

Results: The currently established VII-PT was not sensitive to factor VII and has a similar sensitivity to factor II/X with PT. Factor VII dropped faster than factor II/X in patients taking warfarin and came to the bottom level on the third day after the first dose. PT-INR reached the targeted therapy interval on day 2 but over the upper interval (INR > 3.0) for two days (day 4 ,5) and then backed to the targeted interval. VII-PT-INR reached the targeted therapy interval on day 3 and then within the interval stably.

Conclusion(s): VII-PT and derived VII-PT-INR was demonstrated to overcome the disturbance of factor VII and has the potential to substitute PT-INR to monitor warfarin therapy.