Activation of prothrombin is crucial in physiological and pathological coagulation. Various rare diseases involving prothrombin have been described (e.g., hypoprothrombinemia). Anti-prothrombin antibodies in autoimmune disease may be a factor in the formation of the lupus anticoagulant, also known as antiphospholipid syndrome. Hyperprothrombinemia can be caused by the G20210A mutation. Thus, manipulation of prothrombin is central to the mode of action of most anticoagulants [1].