Coagulation Factor XI: ProductsCoagulation Factor XI is synthesized in the liver and circulates in the plasma as a disulfide bond-linked dimer complexed with High Molecular Weight Kininogen. Factor XI is converted into active XIa either via the contact phase of blood coagulation or through Thrombin-mediated activation on the platelet surface. The resulting XIa converts Coagulation Factor IX into IXa, which subsequently activates Coagulation Factor X (Xa). Xa then can mediate Coagulation Factor II/Thrombin activation. Patients with factor XI deficiency are prone to excessive bleeding after hemostatic challenge.