Also Known As
Anticardiolipin Antibodies, aCL antibody
Formal Name
Cardiolipin Antibodies, IgG, IgM, and IgA
This article was last reviewed on
This article waslast modified on 4 August 2021.
At a Glance
Why Get Tested?

To help investigate unexplained blood clot formation, to help determine the cause of recurrent miscarriage, or as part of an evaluation for antiphospholipid syndrome

When To Get Tested?

When you have had one or more unexplained venous or arterial thrombotic episodes; when you have had recurrent miscarriages, especially in the 2nd and 3rd trimesters

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?


On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

These tests detect the presence of three classes (IgG, IgM, and/or IgA) of cardiolipin antibodies. Produced by the immune system in response to a perceived threat, these proteins are the most common antiphospholipid antibodies. They are acquired autoantibodies that can affect the body’s ability to regulate blood clotting. Although IgA antibodies can be measured by many commercially available laboratory tests, their significance remains unclear and the current UK guidelines do not consider them to be diagnostic for antiphospholipid syndrome.

Cardiolipins, and other related phospholipids, are lipid molecules normally found in cell membranes and platelets. They play an important role in the blood clotting process. When antibodies are produced against cardiolipins, they increase the risk of developing recurrent blood clots (thrombi) in arteries and veins. There is a stronger association for IgG antibodies and venous thrombosis (e.g. deep vein thrombosis), whereas both IgG and IgM may be seen in arterial clots, including acute stroke. Cardiolipin antibodies are also associated with thrombocytopenia, recurrent miscarriages (especially in the 2nd and 3rd trimester), and with premature labour and  pre-eclampsia.

Cardiolipin antibodies are frequently seen with autoimmune disorders, such as Systemic Lupus Erythematosus (SLE), and with other antiphospholipid antibodies, such as lupus anticoagulant. They may also occur temporarily in patients with acute infections, HIV/AIDS, some cancers, with drug treatments (such as phenytoin, penicillin, and procainamide), and asymptomatically in the elderly.

When a patient has thrombi formation, recurrent miscarriages, thrombocytopenia, cardiolipin antibodies, and/or another antiphospholipid antibody, they may be diagnosed with Antiphospholipid Syndrome (APS). APS can be primary with no underlying autoimmune disorder, or secondary, existing with a diagnosed autoimmune disorder.

Accordion Title
Common Questions
  • How is it used?

    Tests for IgG and IgM cardiolipin antibodies are frequently requested to help find the cause of an unexplained thrombotic episode, recurrent miscarriage, or thrombocytopenia. They may be requested with  lupus anticoagulant testing to help investigate the cause of a prolonged PTT (activated partial thromboplastin time), especially if clinical findings suggest that the patient may have  SLE or another autoimmune disorder. If these test results are normal but clinical suspicions still exist, IgA cardiolipin antibody testing may be requested, but their significance has not been confirmed in large studies.

    If one or more of the classes of cardiolipin antibodies is detected, then the test(s) should be repeated at least 12 weeks later to help find whether their presence is persistent or temporary. If a patient with a known autoimmune disorder tests negative for cardiolipin antibodies, they may be retested later, as these antibodies may develop.

  • When is it requested?

    Cardiolipin antibody testing may be requested when a patient has symptoms suggestive of a thrombotic episode, such as pain and swelling in the extremities, acute stroke, shortness of breath, or headaches. It may also be requested when a woman has had recurrent miscarriages, or requested with lupus anticoagulant testing as a follow-up to a prolonged PTT test. When an IgG, IgM, and/or IgA cardiolipin antibody is detected, the test may be repeated several weeks later to determine whether the antibody is temporary or persistent.

    If cardiolipin antibodies are not detected in a patient with an autoimmune disorder, such as SLE, tests may be used in the future to screen for their development.

  • What does the test result mean?

    A negative result means only that the cardiolipin antibody class tested (IgG, IgM, and/or IgA) is not present at this time. Since cardiolipin antibodies are the most common of the antiphospholipid antibodies, it is not unusual to find them for just a short while due to an infection or drug, or present but without symptoms as a person ages. The low concentrations of antibody seen in these situations are usually not important, but they must be considered with the patient’s symptoms and other clinical information.

    Moderate to high levels of one or more of the classes of cardiolipin antibodies that persist when retested more than 12 weeks later indicate the likely continued presence of that specific antibody.

  • Is there anything else I should know?

    Occasionally, cardiolipin testing may be used 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 patients with cardiolipin antibodies.

  • If I have anticardiolipin antibodies, will I definitely develop blood clots?

    No. The cardiolipin antibodies represent a risk factor, but they cannot predict whether an individual will have recurrent blood clots or other associated complications. Also, if a person does have blood clots, the presence of the antibodies cannot predict their frequency or severity, but some patients with multiple antibodies may have more severe problems.

  • Should I tell a new doctor that I have anticardiolipin antibodies?

    Yes, this is an important part of your medical history. Your doctor needs this information even if you are asymptomatic so that they can tailor any procedures or medical treatment around this risk factor.