Antiphospholipid Antibodies

Antiphospholipid antibody tests are used to detect several specific phospholipid-binding proteins that the body produces 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 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, in the elderly and temporarily with infections and with some drug treatments (such as phenothiazines and procainamide).

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. There are two types of tests that are used to detect antiphospholipid antibodies. The first is the test for cardiolipin antibodies used to detect several classes (IgG, IgM, and/or IgA) of the antibodies themselves. The second type is lupus anticoagulant assays, which are functional tests used to detect whether the antibody can block phospholipid-dependent tests. These are tests that measure the time it takes for a patient’s sample to clot, and they require the presence and action of phosopholipids for clotting to occur. Lupus anticoagulant assays begin with an assay to detect prolongation of a phospholipid dependent test, the most common of which is the PTT. Confirmatory studies then need to be performed, preferably with a similar method as the initial screening assay.

Additional diagnostic and confirmatory tests may include RVVT (Russell viper venom time), PNP (platelet neutralization procedure), KCT (kaolin clotting time) and/or hexagonal lipid neutralization test.

A blood sample is obtained by inserting a needle into a vein in the arm.

No test preparation is needed.