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The page below is a sample from the LabCE course Laboratory Evaluation of the Lupus Anticoagulant found in Antiphospholipid Syndrome (APS). Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Dilute Russell Viper Venom Time (dRVVT)

The dilute Russell viper venom (dRVV) test is a snake venom which contains a factor X activating enzyme and a factor V (FV) activator which is strongly phospholipid-dependent. The screening reagent contains RVV, calcium ions, and phospholipids. The venom activates the coagulation cascade at factor X and activates factors below factor X (I, II and V), eliminating any influence of factors above factor X in the coagulation cascade (VIII, IX, XI and XII). As a result, the test is not effected by abnormalities in the contact factors or by deficiencies or inhibitors in factors VIII and IX.
The first part of the assay is a dRVVT screening test which uses a reagent with a low concentration of phospholipids. When there are autoantibodies against phospholipids in the sample they are partly neutralized resulting in a prolonged clotting time. While the confirmatory test uses dRVVT with a higher concentration of phospholipids. This results in a shortened clotting time. The final result is a ratio of the screen and confirm. If the ratio is > 1.2 the result is positive.
Guidelines have suggested performing a normalized ratio and a ratio to eliminate any false positives due to a factor deficiency.
Antibodies to FV or a deficiency of FV will prolong the dRVVT; however, the prolongation will not correct when a correction is performed. This is done by calculating a corrected ratio using pooled normal plasma (PNP). The dRVVT screen is divided by the dRVVT screen of the PNP, as is the dRVVT confirm is divided by the dRVVT confirm of the PNP. In patients on warfarin, the dRVVT is unreliable. Laboratories can perform a 1:1 mix with PNP to correct for the presence of warfarin.
Heparin will also prolong the dRVVT, but this can be detected with in prolongation of the thrombin time. It is important to perform this test to ensure the sample does not contain heparin which may result in a false positive test.