At a glance
Also known as
APL antibodies; APS antibodies
Why get tested?
To help investigate excessive blood clot formation; to help determine the cause of recurrent miscarriage; to evaluate a prolonged PTT (partial thromboplastin time); as part of an evaluation for antiphospholipid antibody syndrome
When to get tested?
If you have a prolonged PTT test; if you have had a recurrent unexplained venous or arterial blood clot; if you have had recurrent miscarriages, especially in the 2nd and 3rd trimesters
A blood sample drawn from a vein in your arm
Test preparation needed?
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 labour, and .
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 recognised 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), lupus anticoagulant and anti-beta-2 glycoprotein 1. Others that are not as frequently tested include anti-phosphatidylserine. While the lupus anticoagulant cannot be tested directly, several classes (, , and/or ) of the other antibodies can be measured. Each of these tests contribute information that either leads toward the confirmation of the presence of clinically significant antiphospholipid antibodies or not. While recent recommendations have emphasised the use of both a lupus anticoagulant test and the anti-beta-2 glycoprotein 1 test for the classification of antiphospholipid syndromes, anticoardiolipin antibodies are also included in the diagnostic work-up. It is likely that IgM antibodies are not pathogenic but they remain in the international consensus criteria until further data is accumulated.
The lupus anticoagulant is detected by performing a panel of clotting based tests that begin with a prolonged APTT (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 APTT 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 neutralisation procedure), KCT (kaolin clotting time) and/or hexagonal lipid neutralisation test.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.