Factor X consumption attenuates the coagulation effect of emicizumab: a case of severe hemophilia A treated with emicizumab and factor VIII-bypassing agents.

In patients with hemophilia A with inhibitor (PwHA-I), emicizumab drastically reduces bleeding events. However, few studies have investigated the behavior and effects of factor X (FX) in patients who require intensive treatment with factor VIII-bypassing agents (BPA) and emicizumab. A 59-year-old man with HA-I receiving emicizumab prophylaxis was admitted to our hospital because of acute gangrenous cholecystitis. He received percutaneous transhepatic gallbladder drainage and laparoscopic cholecystectomy along with repeated administration of recombinant activated factor VII (rFVIIa). On day 10, a large hematoma developed around the residual gallbladder. Rotational thromboelastometry (ROTEM) suggested poor effect of rFVIIa and reduced activity of emicizumab. Considering that this could be due to consumption of FX, plasma-derived FVIIa/FX agent (pdFVIIa/X) was administered, and ROTEM parameters recovered considerably. The patient was discharged on day 19 uneventfully. Plasma assays revealed that FX antigen level (FX:Ag) was 107.5% at baseline but then decreased. Administration of pdFVIIa/FX restored FX:Ag (pre/post 47.2%/125.5%). ROTEM and thrombin generation assay with in vitro addition of anti-emicizumab antibody suggested that low FX:Ag was responsible for attenuating the effect of emicizumab, and pdFVIIa/FX administration restored coagulation potentials. In PwHA-I receiving intensive treatment with rFVIIa under emicizumab prophylaxis, FX consumption might attenuate the effect of emicizumab.