What is being tested?Lupus anticoagulant is a protein that increases the risk of developing blood clots in both the veins and arteries. These clots may block blood flow in any part of the body, leading to
strokes,
heart attacks, pulmonary embolisms, deep vein thrombosis (usually clots in the legs), and to recurrent fetal loss, especially in the 2
nd and 3
rd trimesters (thought to be related to clotting in placental blood vessels). The lupus anticoagulant is an acquired condition. Although it is found most frequently in those with
autoimmune diseases, such as
Systemic Lupus Erythematosus (SLE), the lupus anticoagulant may also be seen in those with infections such as or cancersHIV/AIDS, cancers, and in those with infection,
HIV/AIDS, cancers, and in those who are taking certain medications, such as phenothiazines, procainamide, and fansidar. The antibody is thought to be present in about 1 – 2% of the general population and may develop in people with no known risk factors.
The lupus anticoagulant (LA) is not a diagnostic test for lupus. It gets its name because of its association with SLE. It often prolongs the partial thromboplastin time (PTT) test, a coagulation test that, when prolonged, usually indicates anticoagulation and bleeding, not thrombosis. Lupus anticoagulant prolongs the PTT test, as well as several other related tests, because it binds to phospholipids in the reagents (chemicals) used in performing the PTT test.
In the body, phospholipids play a vital role in the blood clotting process. They are found primarily on the surface of platelets and assist in the activation of several coagulation factors, which are proteins that are sequentially activated in response to blood vessel or tissue damage in a process called the coagulation cascade. The lupus anticoagulant is one of three primary antiphospholipid antibodies that are associated with an increased risk of thrombosis. The others are anticardiolipin antibodies and antibodies against beta-2 glycoprotein 1 (less common), and together they form the antiphospholipid antibody syndrome (also called Hughes syndrome). A person may have one or more of these phospholipid binding antibodies. Each interferes with the clotting process in a way that is not well understood and singly or together, increase a person’s tendency to clot.
While anticardiolipin and anti-beta2-glycoprotein I antibodies may be tested for directly, there is not a single test for the lupus anticoagulant. It is usually diagnosed by using a panel of sequential tests. These tests operate on the principle that the lupus anticoagulant is a nonspecific inhibitor; it does not target a specific coagulation factor but binds to the assay’s phospholipids, inhibiting and prolonging the tests. For more information, see the section titled “What does the test result mean?”
