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Factor VIII (FVIII)
Factor VIII (FVIII) / Anti-haemophilic Factor is an essential X-linked glycoprotein that serves as a critical cofactor in the intrinsic pathway of the blood coagulation cascade, which is the fundamental process for haemostasis. Its deficiency is the underlying cause of Haemophilia A.
- FVIII is synthesized primarily by liver sinusoidal cells and circulates in the plasma in a stable, inactive complex with von Willebrand factor (vWF). The vWF acts as a protective carrier, shielding FVIII from premature degradation.
- The critical function of FVIII occurs after vascular injury: FVIII is activated by proteolytic cleavage (primarily by thrombin, FIIa) to become activated FVIII (FVIIIa). This FVIIIa then binds to activated Factor IX (FIXa) on the surface of activated platelets to form the intrinsic tenase complex (FIXa-FVIIIa).
- This complex exponentially accelerates the activation of Factor X (FX) to activated Factor X (FXa). This FXa is central to the common pathway, leading rapidly to the generation of large amounts of thrombin and the formation of a stable fibrin clot.
Accurate measurement of both FVIII antigen (FVIII:Ag) and its functional activity (FVIII:C) is critical for the diagnosis and classification of the severity of Haemophilia A, as well as for monitoring factor replacement therapy. Products related to FVIII are essential reagents for coagulation testing, clinical research, and the development of assays to detect or quantify FVIII inhibitors (alloantibodies) that can arise in treated Haemophilia A patients.
