Also known as: Anti-cardiolipin antibodies, aCL antibodies
Name: Anti-cardiolipin antibodies, IgG, IgM, IgA
Related tests: Antiphospholipid antibodies, Lupus anticoagulant
Why is the test done?
It helps identify the causes of inappropriate blood clotting or repeated miscarriages, or as part of an assessment for antiphospholipid syndrome.
When to have the test?
If you have had one or more unexplained venous or arterial blood clots, or repeated miscarriages, especially in the second or third trimester
Sample required?
A blood sample from a vein in the arm
What is being measured?
These tests detect the presence of three classes (IgG, IgM and/or IgA) of anti-cardiolipin antibodies. Produced by the immune system in response to a stimulus, these proteins are the most common form of antiphospholipid antibodies. They are autoantibodies that can affect the body’s ability to regulate blood clotting in a way that is not yet fully understood.
Cardiolipins and other related phospholipids are lipid molecules found in cell membranes and platelets. They play an important role in the blood clotting process. When anti-cardiolipin antibodies are produced, they increase the risk of forming clots (thrombi) in both arteries and veins. Anti-cardiolipin antibodies are associated with a low platelet count (thrombocytopenia) and an increased risk of miscarriage (especially in the second and third trimesters), premature birth and pre-eclampsia.
Anti-cardiolipin antibodies are frequently associated with autoimmune disorders such as systemic lupus erythematosus (SLE), and together with other antiphospholipid antibodies such as lupus anticoagulant. They can also be found temporarily in patients with acute infections, HIV/AIDS, some cancers or drug treatments (phenytoin, penicillin, procainamide), and without any symptoms in elderly people. When a patient has blood clots, repeated miscarriages, thrombocytopenia and anti-cardiolipin antibodies (and/or other antiphospholipid antibodies), antiphospholipid syndrome (APS) can be diagnosed. APS can be primary (without other autoimmune disorders) or secondary (together with an already diagnosed autoimmune disorder).
How is the test result used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is the test result used?
Tests measuring IgG and IgM anti-cardiolipin antibodies are usually requested to find the cause of an unexplained thrombotic episode, repeated miscarriages or thrombocytopenia. They may be requested together with the lupus anticoagulant test to help explain a prolonged aPTT (activated partial thromboplastin time), especially if the clinical findings suggest that the patient may have SLE or another autoimmune disorder. If the results of the primary tests are negative but suspicion remains, the IgA anti-cardiolipin test is also requested.
If one or more classes of anti-cardiolipin antibody are detected, the same test(s) will be repeated at least 6 weeks later to determine whether their presence is persistent or temporary. If a patient with a known autoimmune disorder is negative for anti-cardiolipin antibodies, they are measured again later, as these antibodies can develop at any time.
When is it requested?
The anti-cardiolipin antibody test is requested when a patient has symptoms suggesting a thrombotic episode, such as pain and swelling in the limbs, shortness of breath or headache. It may also be requested when a woman has had recurrent miscarriages and/or together with the lupus anticoagulant test to investigate a prolonged aPTT. When an IgG, IgM or IgA anti-cardiolipin antibody is detected, the test is usually repeated several weeks later to determine whether the antibody is persistent or temporary.
If anti-cardiolipin antibodies are not present in a patient with an autoimmune disorder such as SLE, the test will need to be repeated in the future as screening.
What does the test result mean?
A negative result only means that the antibody class tested (IgG, IgM and/or IgA) is not present at that moment. Since anti-cardiolipin antibodies are the most common antiphospholipid antibodies, it is not unusual to find them temporarily raised after an infection or taking medicines, or simply with ageing. The low or moderate antibody concentrations found in these situations are often insignificant, but must be considered together with the patient’s symptoms and other clinical information.
A moderate or high concentration of one or more antibody classes that persists 6 weeks after the first measurement indicates the continued presence of that antibody.
Is there anything else I should know?
Occasionally the anti-cardiolipin antibody test is requested to find the cause of a positive VDRL/RPR test for syphilis. The reagents used for the syphilis test contain phospholipids, which can cause a false positive result in patients with anti-cardiolipin antibodies.
It has recently been recommended to replace anti-cardiolipin antibody testing with the more specific test for antibodies against human beta-2 glycoprotein I (B2-GPI) to detect antiphospholipid antibodies.
1. If I have anti-cardiolipin antibodies, will I definitely get blood clots?
2. Should I tell a new doctor that I have anti-cardiolipin antibodies?
1. If I have anti-cardiolipin antibodies, will I definitely get blood clots?
2. Should I tell a new doctor that I have anti-cardiolipin antibodies?
Yes, it is an important part of your medical history. The doctor needs this information even if you have no symptoms, so that specific treatment can be planned to manage this risk factor.