What is being tested?
Cardiolipin antibodies are autoantibodies produced by the immune system that mistakenly target the body’s own cardiolipins, substances found in the outermost layer of cells (cell membranes) and platelets. These autoantibodies can affect the body’s ability to regulate blood clotting in a way that is not well understood. This test detects the presence of cardiolipin antibodies in the blood.
Cardiolipins, and other related phospholipids, are lipid molecules that play an important role in the blood clotting process. Cardiolipin antibodies target cardiolipins and are associated with an increased risk of developing recurrent inappropriate blood clots (thrombi) in veins and arteries, such as the deep veins of the legs (DVT) or the lungs (pulmonary embolism, PE). They may also be associated with a low platelet count (thrombocytopenia), recurrent miscarriages (especially in the second and third trimester), and with premature labor and pre-eclampsia.
Cardiolipin antibodies are the most common antiphospholipid antibody, a group of autoantibodies associated with excessive clotting and autoimmune diseases, such as lupus. They are frequently detected with other antiphospholipid antibodies, such as lupus anticoagulant and anti-beta-2 glycoprotein 1. They may also be detected temporarily in people with acute infections, HIV/AIDS, some cancers, with drug treatments (such as phenytoin, penicillin, and procainamide), and in the elderly.
When an individual has inappropriate blood clot formation, recurrent miscarriages, cardiolipin antibodies, and/or another antiphospholipid antibody, the person may be diagnosed with antiphospholipid syndrome (APS). APS can be primary or secondary. Primary APS is not necessarily associated with a related autoimmune disorder, while secondary APS is associated with an autoimmune disorder.
How is it used?
Tests for cardiolipin antibodies are frequently used to help determine the cause of:
- An unexplained blood clot (thrombotic episode)
- Recurrent miscarriages
- A prolonged result on the coagulation (clotting test) PTT (partial thromboplastin time); in this setting, the test is often ordered along with lupus anticoagulant testing (e.g., dilute Russell viper venom test, DRVVT)
If cardiolipin antibodies are detected on an initial test, then it is usually repeated 12 weeks later to help determine whether their presence is persistent or temporary. If a person with a known autoimmune disorder tests negative for cardiolipin antibodies, they may be retested later as these antibodies may develop at any time in the future.
There are three classes of cardiolipin antibodies that may be present in the blood: IgG, IgM and/or IgA. The two most commonly tested are IgG and IgM. However, if these tests are negative and clinical suspicions still exist, then IgA cardiolipin antibody testing may be ordered.
Some other tests that may be performed in conjunction with cardiolipin antibody tests include lupus anticoagulant testing (e.g., DRVVT) and anti-beta-2 glycoprotein 1 antibody.
When is it ordered?
Cardiolipin antibody testing is typically ordered as part of excessive clotting workup when an individual has symptoms suggestive of a blood clot (thrombotic episode), especially when they recur. Signs and symptoms vary, depending on the location of the clot.
If the clot is in the deep veins of the legs (deep vein thrombosis, DVT), a person may have symptoms such as:
- Leg pain or tenderness, usually in one leg
- Leg swelling, edema
- Discoloration of the leg
If the clot is affecting the lungs (pulmonary embolism), a person may have symptoms such as:
- Sudden shortness of breath, labored breathing
- Coughing, hemoptysis (blood present in sputum)
- Lung-related chest pain
- Rapid heart rate
Testing may also be ordered when a woman has had recurrent miscarriages and/or ordered along with lupus anticoagulant testing as a follow-up to a prolonged PTT test. When cardiolipin antibody is detected, then the test may be repeated several weeks later to determine whether the antibody is temporary or persistent.
The test for cardiolipin antibodies may also be ordered when an individual has signs and symptoms of an autoimmune disorder and/or has a positive result on an ANA test, as the test may provide the health care practitioner with additional information to help establish a diagnosis. If cardiolipin antibodies are not detected in a person with a diagnosed autoimmune disorder such as lupus, then tests may be ordered in the future to screen for their development.
What does the test result mean?
A negative result means only that cardiolipin antibodies are not present or not present at a detectable level in the blood at the time of the test.
Cardiolipin antibodies are the most common of the antiphospholipid antibodies. It is not unusual to detect them in a person’s blood temporarily due to an infection or drug, or in people without symptoms as they age. The low to moderate amounts of antibody seen in these situations are frequently not significant, but they must be evaluated in conjunction with any signs, symptoms, and/or other clinical information.
Moderate to high levels of cardiolipin antibodies that persist when tested again 12 weeks later indicate the likely continued presence of that specific antibody, which may be associated with an increased risk of excessive clotting or recurrent miscarriages.
Is there anything else I should know?
Occasionally, cardiolipin testing may be ordered to help determine the cause of a positive VDRL/RPR test for syphilis. The reagents used to test for syphilis contain phospholipids and can cause a false-positive result in those with cardiolipin antibodies.
If I have cardiolipin antibodies, will I definitely develop blood clots?
Not necessarily. The cardiolipin antibodies represent a risk factor, but they cannot predict whether an individual person will have recurrent blood clots or other associated complications. And, if a person does have blood clots, the presence of the antibodies cannot predict their frequency or severity.
Should I tell a new healthcare provider that I have cardiolipin antibodies?
Yes, this is an important part of your medical history. Your health care providers need this information, even if you are asymptomatic, so that they can tailor any procedures or medical treatment plans around this risk factor.
The Lupus Foundation of America: Antiphospholipid Antibody Syndrome
March of Dimes: Pregnancy Complications, Thrombophilias
APS Foundation of America
National Human Genome Research Institute: Learning About Antiphospholipid Syndrome (APS)