Emicizumab (Hemlibra®) is a subcutaneous hemostatic treatment approved in 2019 for the prophylaxis in severe hemophilia A. Emicizumab is a bispecific monoclonal antibody mimicking factor VIIIa that provides a constant level of coagulation similar to that observed in minor haemophilia A patients whose factor VIII level is 10-15%. Although the correction of plasma coagulation in vivo is only partial, emicizumab strongly shortens the in vitro coagulation times involving the intrinsic pathway such as aPTT(activated partial thromboplastin time).

The investigators will evaluate the effect of emicizumab on a coagulation test (Activating clotting time (ACT i-STAT Alinity)) used as a point of care device to monitor heparin therapies during cardiac surgeries (cardiopulmonary bypass) and cardiac catheterizations. Because ACT is activated through the intrinsic pathway, it may also be shortened by emicizumab. Prophylactic treatment with emicizumab would make it impossible to use ACT for heparin therapy in a hemophiliac patient benefiting from this treatment.

The aim of this in vitro study is to assess the effect of emicizumab on the in vitro heparin-induced ACT increase in severe hemophilia A patients treated with emicizumab and in healthy volunteers (measurement on the i- STAT Alinity) thanks to in vitro blood spiking experiments.

Some data have already been published with other ACT devices (Hemochron..) but never with the i-STAT Alinity device which uses a different technology and other reagents.

Inclusion criteria:

• severe hemophiliacs under emicizumab ( > 4 weeks)

Exclusion Criteria:

• infusion of factor VIII < 5 days
• patients refusing to participate in the study
• protected persons
• anticoagulants

see above