This in vitro diagnostic test is based on the ability of the<unk>  of the<unk> i<unk>  to accelerate blood clotting. The<unk>  contains the enzymes RVV-V and RVV-X which activate factor V and factor X, which converts prothrombin into thrombin in the presence of phospholipid and calcium. In the<unk>  assay, low, rate-limiting concentrations of both<unk> 's<unk><unk>  and phospholipid are used to give a standard clotting time of 30 to 40 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 be significantly shortened if there was only a deficiency of coagulation factors alone. A prolonged clotting time beyond a 3SD (or 95th percentile) cutoff that does not correct despite the mixing study suggests the presence of a lupus anticoagulant. An abnormal result for the initial<unk>  assay should be followed by a<unk>  confirmatory test. In this test, the inhibitory effect of lupus anticoagulants on phospholipids in the<unk>  can be overcome by adding an excess of phospholipid to the assay. The clotting times of both the initial<unk>  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<unk>  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<unk>  mainly activates only factors V and X. However<unk>  tests are strongly affected by the new direct oral anticoagulants (DOACs) and false positive LA results are obtained particularly with rivaroxaban. It is now possible to specifically remove DOACs from test plasmas with activated carbon and enable the correct diagnosis of LA with the<unk>  system despite their initial presence.
Dilute Russell's viper venom time
Kaolin clotting time
Urine anion gap
Thrombin time
CSF tap test
Rapid plasma reagin
Activated clotting time
Partial thromboplastin time