What is being tested?Antiphospholipid antibody tests are used to detect specific
autoantibodies, proteins the body creates against itself in an autoimmune response to phospholipids. Found in cell membranes and platelets, phospholipids are a normal part of the body. They are lipid molecules that play a crucial role in blood clotting. When antiphospholipid antibodies are produced, they interfere with the clotting process in a way that is not fully understood. They increase an affected patient’s risk of developing recurrent inappropriate blood clots (thrombi) in arteries and veins, which can lead to
strokes and
heart attacks. Antiphospholipid antibodies are also associated with thrombocytopenia (decreased platelets) and with the risk of recurrent miscarriages (especially in the 2nd and 3rd trimester), premature labor, and
pre-eclampsia.
One or more antiphospholipid antibodies are frequently seen with autoimmune disorders such as Systemic Lupus Erythematosus (SLE). They may also be seen with HIV, some cancers, temporarily with infections and some drug treatments (such as phenothiazines and procainamide), and in the elderly. Antiphospholipid syndrome (APS), also called Hughes syndrome, is a recognized group of signs and symptoms that includes the formation of thrombi, miscarriages, thrombocytopenia, and the presence of one or more antiphospholipid antibodies. APS can be primary (with no underlying autoimmune disorder) or secondary (existing with a diagnosed autoimmune disorder).
The most common antiphospholipid antibodies are cardiolipin antibodies (also called anticardiolipin antibodies) and the lupus anticoagulant. Others that are not as frequently tested include anti-beta2 glycoprotein I and anti-phosphatidylserine. While the lupus anticoagulant cannot be tested directly, several classes (IgG, IgM, and/or IgA) of the other antibodies can be measured. Each of these tests contributes information that either leads toward the confirmation of the presence of clinically significant antiphospholipid antibodies or not. While recent recommendations have emphasized the use of both a lupus anticoagulant test and the anti-beta2 glycoprotein I test for the classification of antiphospholipid syndromes, there is evidence that anticoardiolipin antibodies should still be part of the diagnostic work-up.
The lupus anticoagulant is detected by performing a panel of tests that begin with a prolonged PTT (which indicates the presence of a substance interfering with the clotting process), followed by a mixing study in which patient plasma and normal plasma are mixed, to confirm that the prolongation of PTT is due to inhibitor and not to a deficiency of coagulation factors. Confirmatory studies need to be performed, preferably with a similar method as the initial screening assay. These confirmatory tests may include RVTT (Russell viper venom time), PNP (platelet neutralization procedure), KCT (kaolin clotting time) and/or hexagonal lipid neutralization test.
