Lupus anticoagulant

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Lupus anticoagulant is the concept that an autoantibody can cause prolongation of clotting times. The presence of prolonged clotting times often triggers functional testing of the blood clotting function, as well as serological testing to identify common autoantibodies. Therefore, a lupus anticoagulant is the phenomenon where antibodies bind to phospholipids and proteins associated with the cell membrane, and interfere with in-vitro tests of clotting function. This antibody has the peculiar nature of causing a delay in coagulation in phospholipid-dependent laboratory tests such as the partial thromboplastin time. Paradoxically, lupus anticoagulants are risk factors for thrombosis. It is also known as lupus antibody, LA and lupus inhibitor. Conceptually, lupus anticoagulants overlap with the antiphospholipid antibody syndrome.

The name "lupus anticoagulant" is a misnomer. Most patients with a lupus anticoagulant do not actually have lupus erythematosus, and only a small proportion will proceed to develop this disease (which causes joint pains, skin problems and renal failure, amongst other complications). Patients with lupus erythematosus are more likely to develop a lupus anticoagulant than the general population.

Patients with a lupus anticoagulant are prone to thrombosis and habitual abortion (repeated miscarriage).

The initial workup of a prolonged PTT is a mixing study, also known as a 50:50 inhibitor screen. This test determines whether a clotting inhibitor, such as a lupus anticoagulant, is present. The mixing study may also "correct" with the addition of normal plasma, in which case the diagnosis is a clotting factor deficiency, not a clotting inhibitor such as a lupus anticoagulant. Diagnosis of a lupus anticoagulant is then confirmed with phospholipid-sensitive functional clotting testing, such as the dilute Russell's viper venom time, or the Kaolin clotting time. Excess phospholipid will eventually correct the prolongation of these prolonged clotting tests (conceptually known as "phospholipid neutralization" in the clinical coagulation laboratory), confirming the diagnosis of a lupus anticoagulant.

Treatment for a lupus anticoagulant is usually undertaken in the context of documented thrombosis, such as extremity phlebitis or dural sinus vein thrombosis. Patients with a well-documented (i.e., present at least twice) lupus anticoagulant and a history of thrombosis should be considered candidates for indefinite treatment with blood thinners. Patients with no history of thrombosis and a lupus anticoagulant should probably be observed. Current evidence suggests that most of the risk of recurrent thrombosis in patients with a antiphospholipid antibody is accountable due to the presence of anti-beta2-glycoprotein 1 antibodies and anticardiolipin antibodies, and less so from the presence of a lupus anticoagulant on functional testing.

Miscarriages can be prevented with the administration of low molecular weight heparins (LMWHs), and thrombosis is treated with anticoagulants (LMWHs and warfarin).^[1]

[edit] References

^ Dolitzky M, Inbal A, Segal Y, Weiss A, Brenner B, Carp H (2006). "A randomized study of thromboprophylaxis in women with unexplained consecutive recurrent miscarriages". Fertil Steril 86 (2): 362-6. PMID 16769056.