<P> This 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 . In the dRVVT assay , low , rate - limiting concentrations of both Russell 's viper venom and phospholipid are used to give a standard clotting time of 23 to 27 seconds . 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 . A mixing study is then performed , which consists of adding an equal volume of the patient 's plasma to normal plasma ; in this study , one would expect the clotting time to return to the normal range if there was only a deficiency of coagulation factors alone . A prolonged clotting time of 30 seconds or greater that does not correct despite the mixing study suggests the presence of a lupus anticoagulant . An abnormal result for the initial dRVVT assay should be followed by a dRVVT confirmatory test . In this test , the inhibitory effect of lupus anticoagulants on phospholipids in the dRVVT can be overcome by adding an excess of phospholipid to the assay . The clotting times of both the initial dRVVT assay and confirmatory test are normalized and then used to determine a ratio of time without phospholipid excess to time with phospholipid excess . In general , a ratio of greater than 1.3 is considered a positive result and implies that the patient may have antiphospholipid antibodies . The dRVVT test has a higher specificity than the aPTT test for the detection of lupus anticoagulant , because it is not influenced by deficiencies or inhibitors of clotting factors VIII , IX or XI as the venom only activates factors V and X . </P>
<P> This 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 . In the dRVVT assay , low , rate - limiting concentrations of both Russell 's viper venom and phospholipid are used to give a standard clotting time of 23 to 27 seconds . 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 . A mixing study is then performed , which consists of adding an equal volume of the patient 's plasma to normal plasma ; in this study , one would expect the clotting time to return to the normal range if there was only a deficiency of coagulation factors alone . A prolonged clotting time of 30 seconds or greater that does not correct despite the mixing study suggests the presence of a lupus anticoagulant . An abnormal result for the initial dRVVT assay should be followed by a dRVVT confirmatory test . In this test , the inhibitory effect of lupus anticoagulants on phospholipids in the dRVVT can be overcome by adding an excess of phospholipid to the assay . The clotting times of both the initial dRVVT assay and confirmatory test are normalized and then used to determine a ratio of time without phospholipid excess to time with phospholipid excess . In general , a ratio of greater than 1.3 is considered a positive result and implies that the patient may have antiphospholipid antibodies . The dRVVT test has a higher specificity than the aPTT test for the detection of lupus anticoagulant , because it is not influenced by deficiencies or inhibitors of clotting factors VIII , IX or XI as the venom only activates factors V and X . </P>
dilute russell 's viper venom test ( drvvt ) which coagulation factor is activated by the venom
dilute russell 's viper venom test ( drvvt ) which coagulation factor is activated by the venom
factor V factor X
factor V factor X