Investigation to distinguish between pregnancy acquired hemophilia A and lupus anticoagulant?: (A) Factor 8 assay, (B) dRVVT, (C) von Willlebrand Factor assay, (D) aPTT
Answer is B. In some cases of pregnancy there is antibody formation against the clotting factors, paicularly against factor 8. Dilute Russell's viper venom time- -In-vitro diagnostic test is based on the ability of the venom of the Russell's 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 Russell's 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.