Chromogenic Factor VIII Assay for Patients with Hemophilia A and on Emicizumab Therapy

This chapter will describe a method for measuring endogenous and infused Factor VIII (FVIII) in patients on emicizumab therapy (Hemlibra, Genetec, Inc). Emicizumab is a bispecific monoclonal antibody used in patients with hemophilia A, with or without inhibitors. The mechanism of action for emicizumab is novel and mimics the role that FVIII plays in vivo by binding and bridging FIXa and FX. It is vital that the laboratory understands the effect this drug has on coagulation tests and uses a suitable chromogenic assay which is not affected by emicizumab, for determination of FVIII coagulant activity and inhibitors.