I [Geo] received a communication from Dr. Pall Onundarson, Hematology Laboratory and Thrombosis and Hemostasis Service, Faculty of Medicine, University of Iceland, Reykjavik, Iceland, about the Fiix-PT assay designed to monitor vitamin K antagonist [warfarin, Coumadin] therapy unaffected by reductions in FVII and FIX which the authors claim to play little role in clinical anticoagulation. I've attached two articles that describe the assay in detail. Dr. Onundarson speculates the assay could also be adapted to anti-Xa DOAC measurement.
Onundarson PT , Palsson R, Witt DM, Gudmundsdottir BR. Replacement of traditional prothrombin time monitoring with the new Fiix prothrombin time increases the efficacy of warfarin without increasing bleeding. A review article. Thrombosis Journal 2021: https://doi.org/10.1186/s12959-021-00327-1.
Oskarsdottir AR, Gudmundsdottir BR, Jensdottir HM, et al. Ignoring instead of chasing after coagulation factor VII during warfarin management: an interrupted time series study. Blood. 2021; 137: 2745–55. doi: 10.1182/blood.2020008698: 10.1182/blood.2020008698.