Emicizumab is a bispecific antibody that targets Factors IXa and X. It mimics Factor VIIIa cofactor activity and is used for prophylaxis in patients with hemophilia A. Its presence can interfere with aPTT-based assays.
Emicizumab bridges Factor IXa and Factor X of human origin only.
Manifestations:
(1) shortening of the aPTT
(2) marked increase in Factor VIII activity measured by aPTT one-stage methods
(3) decrease in Factor VIII inhibitor levels or false negative result
Duration of effect: up to 6 months after a dose
If a patient has received emicizumab then it is necessary to:
(1) switch to an assay not affected by the antibody such as a chromogenic or immunoassay-based assays.
(2) pretreat the plasma sample with anti-emicizumab monoclonal antibodies to inactivate it
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