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This test system is designed for the qualitative detection of lupus anticoagulants (LA) in plasma.6
False-positive dRVVT screen and confirm results may occur in the presence of direct Xa inhibitor or direct thrombin inhibitor anticoagulants or in the presence of warfarin. The dRVVT may be prolonged in patients with deficiencies or inhibitors of factors X, V, II, and fibrinogen. Patients on warfarin will have extended dRVVT results.7 Plasma heparin levels >1 IU/mL may interfere with this test.8 Platelets are a rich source of phospholipid that can neutralize LA. Improper preparation of the platelet-poor plasma at collection reduces the sensitivity of this assay for LA. Due to the heterogeneity of LA antibodies, no single assay will identify all cases.6
Low phospholipid reagent consisting of Russell viper venom with excess calcium is mixed with patient plasma. The time to clot formation is measured photo-optically.
Russell viper venom directly activates factor X in the patient's plasma. Relatively common deficiencies or inhibitors of factors VII, VIII, IX, XI, and XII do not affect the dRVVT assay. Activated factor X (Xa) forms a complex with activated factor V (Va) in the presence of phospholipid. This prothrombinase complex converts factor II (prothrombin) to IIa (thrombin). Thrombin, in turn, cleaves fibrinogen to fibrin leading to detectable clot formation. The dRVVT reagent contains a heparin inhibitor, which makes the test system insensitive to heparin levels up to 1 IU/mL.8 Lupus anticoagulants (LA) are nonspecific inhibitors of phospholipid-dependent, in vitro coagulation tests. The dRVVT reagent is diluted to ensure that it has a low phospholipid concentration, increasing the sensitivity for LA.6
The International Society on Thrombosis and Haemostasis (ISTH) has established criteria for the diagnosis of lupus anticoagulants. The ISTH has defined the minimum diagnostic criteria for LA to include:9,10
• A prolonged clot time in a screening assay such as aPTT-LA and/or dRVVT
• Mixing studies indicating the presence of an inhibitor
• Positive confirmatory studies defining phospholipid dependence of the inhibitor
• No evidence of other coagulopathies through the use of specific factor assays if the confirmatory step is negative or there is evidence of a specific factor inhibitor.
Plasma (platelet poor), frozen
Citrated plasma samples should be collected by double centrifugation. Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio.2,3 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples, except when using a winged blood collection device (ie, "butterfly"), in which case a discard tube should be used.4,5 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternate anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells. Deliver to a plastic transport tube, cap, and recentrifuge for 10 minutes. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube. Transfer the plasma into a LabCorp PP transpak frozen purple tube with screw cap (LabCorp N° 49482). Freeze immediately and maintain frozen until tested. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.
Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.
Causes for Rejection
If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted. Refer to Coagulation Collection Procedures for directions.
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|117887||Dilute Russell's Viper Venom||6303-2||117891||dRVVT||sec||6303-2|