LA Check, DRVVT Screeningsreagens

CRYOcheck LA Check is a dilute Russell’s Viper Venom Time (dRVVT) reagent intended to screen for the presence of lupus anticoagulants (LA) in citrated human plasma.

LA are autoantibodies of the IgG and IgM types which are specifically directed against negatively charged phospholipids, such as phosphatidylinositols and phosphatidylserines, or complexes of phospholipids with either B2-glycoprotein-1 or clotting factors such as prothrombin. They occur in various clinical conditions, especially autoimmune diseases. LA have traditionally been detected using phospholipid sensitive in vitro clotting tests, such as the activated partial thromboplastin time (APTT), kaolin clotting time (KCT) and dRVVT. The dRVVT was introduced in 1986 and showed improved sensitivity to LA over the APTT partially due to a reduced phospholipid concentration.
LA are usually indicated by a prolonged clotting time result that is not corrected by mixing patient plasma with normal plasma. The correction of a prolonged result by the addition of phospholipids to the plasma is a more specific characteristic of LA.
LA prolong phospholipid-sensitive clotting tests, however they are paradoxically associated with thrombotic problems. LA are the most common cause of an unexplained prolonged APTT screening test in the laboratory and need to be carefully distinguished from idiopathic antibodies against factor VIII which can cause bleeding.
LA are now considered to be a significant risk factor in patients with otherwise unexplained thrombosis and are often present in women who have recurrent fetal loss. They are also associated with a variety of hemostatic problems such as thrombocytopenia and neurological disorders.
Russell’s Viper venom directly activates factor X, bypassing factor VII of the extrinsic pathway and the contact and antihemophilic factors of the intrinsic pathway. Therefore dRVVT tests are more specific for LA than APTTs as they are not affected by contact factor abnormalities or by factor VIII deficiencies or antibodies.