Lupus anticoagulant

Lupus anticoagulant (also known as lupus antibody, LA, or lupus inhibitors) is an immunoglobulin that binds to phospholipids and proteins associated with the cell membrane. It is important to note that this disease name is actually a misnomer. Lupus anticoagulant is actually a prothrombotic agent, that is, presence of Lupus anticoagulant antibodies precipitates the formation of thrombi in vivo. Their name derives from their properties in vitro, since in laboratory tests, presence of these antibodies causes an increase in aPTT. It is speculated that the presence of the antibodies interferes with phospholipids utilized to induce in vitro coagulation.

In vivo, it is thought to interact with platelet membrane phospholipids, increasing adhesion and aggregation of platelets; thus its in vivo prothrombotic characteristics.

Terminology
Both words in the term "lupus anticoagulant" can be misleading:


 * 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..


 * The term "anticoagulant" accurately describes its function in vitro, but in vivo, it is now known that it functions as a coagulant.

Workup
The presence of prolonged clotting times on a routine plasma test often triggers functional testing of the blood clotting function, as well as serological testing to identify common autoantibodies such as antiphospholipid antibodies. These antibodies tend to delay in-vitro coagulation in phospholipid-dependent laboratory tests such as the partial thromboplastin time.

The initial workup of a prolonged PTT is a mixing test whereby the patient's plasma is mixed with normal pooled plasma and the clotting is re-assessed. If a clotting inhibitor such as a lupus anticoagulant is present, the inhibitor will interact with the normal pooled plasma and the clotting time will remain abnormal. However, if the clotting time of the mixed plasma corrects towards normal, the diagnosis of an inhibitor such as the lupus anticoagulant is excluded; the diagnosis is a deficient clotting factor that is replenished by the normal plasma.

If the mixing test indicates an inhibitor, 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
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 anticoagulants. Patients with no history of thrombosis and a lupus anticoagulant should probably be observed. Current evidence suggests that the risk of recurrent thrombosis in patients with an antiphospholipid antibody is enhanced whether that antibody is measured on serological testing or functional testing. The Sapporo criteria specify that both serological and functional tests must be positive to diagnose the antiphospholipid antibody syndrome. .

Miscarriages may be more prevalent in patients with a lupus anticoagulant. Some of these miscarriages may potentially be prevented with the administration of aspirin and unfractionated heparin. See the Cochrane Database of Systematic Reviews http://apps.who.int/rhl/reviews/CD002859.pdf, and consult an obstetrician for specific medical advice.

Thrombosis is treated with anticoagulants (LMWHs and warfarin).