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Lupus Anticoagulant Testing

The Lupus Anticoagulant (LA), also referred to as Lupus-like Anticoagulant or Anti-Cardiolipin Antibody, is a heterogeneous group of antibodies which target phospholipids. It usually prolongs the APTT when a sensitive reagent is used. However, there are many APTT reagents on the market today that are relatively insensitive to these antibodies. It may also inhibit the clotting times of some or all of the intrinsic pathway clotting factors (FVIII, FIX, FXI, and FXII). Because the Lupus anticoagulant is heterogeneous, the recommendation for laboratory diagnosis always includes the use of more than one test. The ISTH Subcommittee on Lupus Anticoagulant recommends performing tests utilizing dilute phospholipid with confirmation by the addition of a concentrated phospholipid and an antiphosopholipid antibody test such as anticardiolipin antibody or anti-beta2 glycoprotein1.

Machaon Diagnostics utilizes the following tests:

First: An APTT performed using PTT-LA reagent - a dilute, LA sensitive reagent. If this test is prolonged we suggest:
1. A Thrombin Clotting Time (TCT) to rule out heparin which will cause prolongation of all APTTs and false positives in some of the LA tests. If normal we proceed with:
2. Mixing studies performed with frozen, pooled normal plasma that is platelet free (<5,000 platelets/痞)
3. APTT performed with an insensitive reagent and compared to the PTT-LA utilizing an "index"
4. It is also important to perform a Prothrombin Time as patients with a Lupus Anticoagulant may bleed if they have developed a LA associated Inhibitor to Factor II.

Second: Dilute Russell Viper Venom Test (dRVVT), with the addition of a confirmatory reagent when prolonged.

Third: Anticardiolipin Antibody (IgG, IgM, and IgA) using the original method of Nigel Harris

Other tests available for use in difficult to diagnose patients or further differentiation of positive patients include Anti-beta2 Glycoprotein 1 (b2 GP1), Antiphosphatidylserine and other phospholipid specific tests.