<prompt> A patient is admitted with 3rd episode of deep venous thrombosis. There is no history of any associated medical illness. All of the following investigations are required for establishing the diagnosis except :Protein C deficiencyAntithrombin III deficiencyAntibodies to factor VIIIAntibodies to cardiolipin  <response>: Answer is C Antibodies to factor VIII Antibodies to factor VIII should be suspected in a disorder presenting with bleeding and not in presenting with recurrent thrombosis. Antibodies against factor VIII should be suspected in any acquired severe bleeding disorder associated with a prolonged PTT -- CMDT Factor VIII antibodies are distinguished from lupus anticoagulant by presence of clinical bleeding. Major coagulation defects associated with venous thrombosis Factor V leiden commonest association with DVT Antithrombin III deficiency Protein C deficiency Protein S deficiency Prothrombin gene mutation Homocyteinemia Antiphospholipid antibody Homocyteinemia and Antiphospholipid antibodies are also associated with aerial thrombi others being associated with venous thrombosis only. 