dRVVT test (Dilute Russell’s viper venom time) test
Confirmatory tests for lupus anticoagulants (LA).
Some hematologists recommend doing both the tests because in any one individual with LA, one of these confirmatory tests may be positive, whereas the other is not abnormal owing to the heterogeneity of the LAs. Russell viper venom directly activates factor X and thereby bypasses the factors required in the intrinsic pathway of coagulation. dRVVT is performed similar to aPTT, except intrinsic coagulation factors proximal to factor X are not required and less phospholipids are present in the reaction.
Therefore, the dRVVT test is not affected by factor deficiencies and is more sensitive in the detection of LA than prolongation of the aPTT test. If the dRVVT test is prolonged, it is repeated with excess phospholipid added. In patients with LA, the excess phospholipid will neutralize LA and normalize the dRVVT test. A ratio of dRVVT/dRVVT plus phospholipid of >1.2 is diagnostic of LA.