Factor VIIIa

**Definition:** Activated form of factor VIII. The B-domain of factor VIII is proteolytically cleaved by thrombin to form factor VIIIa. Factor VIIIa exists as a non-covalent dimer in a metal-linked (probably calcium) complex and functions as a cofactor in the enzymatic activation of factor X by factor IXa. Factor VIIIa is similar in structure and generation to factor Va.

**Tree numbers:** - D12.776.124.125.350.300 - D23.119.350.300

**Synonyms:** - Factor Eight A - Blood Coagulation Factor VIII, Activated - Factor 8A - Factor VIII, Thrombin-Activated - Coagulation Factor VIIIa - Factor VIII, Activated