Also known as: Anti-cardiolipin antibodies, anti-beta2 glycoprotein I antibodies, anti-phosphatidylserine antibodies, lupus anticoagulant, LA
Name: Lupus anticoagulant panel, anti-cardiolipin antibodies
Related tests: aPTT, Anti-cardiolipin antibodies, Lupus anticoagulant
Why is the test done?
To investigate inappropriate blood clotting; to find the cause of miscarriages; to assess the meaning of a prolonged aPTT; as part of an assessment for antiphospholipid antibody syndrome.
When is the test done?
If there is a prolonged aPTT; if there have been repeated, unexplained episodes of blood clotting; if there have been repeated miscarriages, especially in the 2nd and 3rd trimesters
Sample required?
A blood sample taken from a vein in the arm
What is being tested?
Antiphospholipid antibody testing is used to detect specific autoantibodies, proteins that the body produces against itself in an autoimmune response against phospholipids. Present in cell and platelet membranes, phospholipids are a normal component 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 ways that are not yet fully understood. In the affected patient they increase the risk of inappropriate clots (thrombi) forming in arteries and veins, which can lead to strokes and heart attacks. These antibodies are associated with thrombocytopenia (a low platelet count) and with the risk of recurrent miscarriages (especially in the 2nd and 3rd trimesters), premature birth and pre-eclampsia.
Antiphospholipid antibodies are frequently found in autoimmune disorders such as systemic lupus erythematosus (SLE). They are also found in HIV, some cancers, temporarily in infections and with drug treatments (such as phenothiazines and procainamide), and in elderly people. Antiphospholipid antibody syndrome (APS), also called Hughes syndrome, is a group of signs and symptoms, occurring alone or together, including blood clots, miscarriages and thrombocytopenia.
APS can be primary (with no autoimmune disorders) or secondary (alongside a diagnosed autoimmune disorder).
The most common of these autoantibodies are anti-cardiolipin antibodies and lupus anticoagulant. Others tested less often are anti-beta2 glycoprotein I and anti-phosphatidylserine antibodies. While lupus anticoagulant cannot be measured directly, several classes (IgG, IgM and IgA) of the other autoantibodies can be measured. Each of these tests adds information that helps confirm or rule out the presence of clinically significant autoantibodies. While recent guidelines have recommended using lupus anticoagulant and anti-beta2 glycoprotein I to classify antiphospholipid syndrome, there is evidence suggesting that anti-cardiolipin is part of the diagnosis.
Lupus anticoagulant is detected with a panel of tests starting with a prolonged aPTT (which indicates the presence of a substance interfering with clotting), followed by a study of the patient’s plasma mixed with normal plasma, to confirm that the prolonged aPTT is due to an inhibitor and not to a deficiency of clotting factors. The confirmatory test should ideally be carried out with methods similar to the initial test. These tests may include the dRVVT (dilute Russell’s viper venom time), PNP (platelet neutralisation procedure), KCT (kaolin clotting time) and the hexagonal phase phospholipid neutralisation test.
How is it used?
When is it requested?
What do the results mean?
Is there anything else I should know?
How is it used?
Antiphospholipid antibody testing is used to find the cause of unexplained thrombotic episodes, recurrent miscarriages, thrombocytopenia and a prolonged aPTT. Depending on the patient’s clinical findings, the doctor may request one or more types of test to detect antiphospholipid antibodies and diagnose APS. Anti-cardiolipin antibodies (IgG, IgM and sometimes IgA) are often requested because the test is widely available. If a patient has a prolonged aPTT, a lupus anticoagulant test is indicated. Anti-beta2 glycoprotein I and anti-phosphatidylserine are requested together with the other tests to detect their presence and provide further information.
If an antiphospholipid antibody is found, the test is repeated 8-10 weeks later to check whether its presence is persistent or temporary. If a patient with an autoimmune disorder tests negative, they should be tested again, as they may develop the autoantibodies later.
When is it requested?
Antiphospholipid antibodies may be requested when the patient has symptoms suggesting thrombotic episodes, such as pain and swelling in the limbs, shortness of breath and migraines. They may be requested when a woman has had frequent miscarriages and as a follow-up to a prolonged aPTT. If one of the tests is positive, it should be repeated a few weeks later to make sure it is not a temporary finding. Antiphospholipid antibody testing is done when there are signs of antiphospholipid antibody syndrome. When a patient with an autoimmune disorder tests negative for antiphospholipid antibodies, one or more tests should be repeated later to check whether autoantibodies have developed.
What do the results mean?
Particular care must be taken in interpreting the test. A negative result only means that no autoantibodies are present at that particular moment. Low or moderate levels of antibodies may be present because of infections or medicines, or because of age. These concentrations are not considered significant but must be assessed together with the patient’s symptoms and clinical information. Sometimes the patient may have one or more classes of a specific antibody. For example, there may be significant amounts of IgG and IgM anti-cardiolipin, or only the less often tested IgA. Moderate and high levels of one or more autoantibodies that persist when retested 8-10 weeks later indicate the constant presence of these antibodies.
If the test shows lupus anticoagulant and it persists on retesting, the patient probably has this condition. Patients with antiphospholipid antibodies and confirmed antiphospholipid syndrome have an increased risk of recurrent thrombotic episodes, miscarriages and thrombocytopenia. The test results do not indicate how often complications will occur, or the type or severity of the condition in the individual patient. Some have many recurrent problems while others have no symptoms. Examples are patients without symptoms who are found to have antiphospholipid antibodies because of a prolonged aPTT measured for other reasons (such as pre-admission tests), or elderly people without symptoms who develop autoantibodies.
Is there anything else I should know?
Occasionally antiphospholipid antibody testing may be requested to find the cause of a positive VDRL. The reagents used for the syphilis test contain phospholipids and can cause a false positive result when specific antibodies are present.
Is there anything that can be done to prevent or eliminate antiphospholipid antibodies?
No. The process that causes them to develop is not fully understood. There are controllable risk factors, such as smoking and obesity, that can increase the risk of thrombosis. Eliminating these factors reduces the risk of thrombosis.