<prompt> Investigation to distinguish between pregnancy acquired hemophilia A and lupus anticoagulant?Factor 8 assaydRVVTvon Willlebrand Factor assayaPTT  <response>: In some cases of pregnancy there is antibody formation against the clotting factors, paicularly against factor 8. Dilute Russells viper venom time- -In-vitro diagnostic test is based on the ability of the venom of the Russells viper to induce thrombosis. -The venom contains some substances RVV-V and RVV-X which directly activate factor V and factor X which turns prothrombin into thrombin in the presence of phospholipid and calcium. -This makes the test sensitive to the presence of lupus anticoagulants, because these antibodies interfere with the clot-promoting role of phospholipid in vitro, and their presence results in a prolonged clotting time. NOTE - the dilute Russells viper venom test and the hexagonal-phase phospholipids test will be Negative in patients with an acquired inhibitor and Positive in patients with lupus anticoagulants. 