• Also Known As:
  • Anticardiolipin Antibodies
  • aCL Antibody
  • Formal Name:
  • Cardiolipin Antibodies (IgG
  • IgM
  • and IgA)
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At a Glance

Why Get Tested?

To help investigate inappropriate blood clot formation, to help determine the cause of recurrent miscarriage, or as part of an evaluation for antiphospholipid syndrome or sometimes other autoimmune diseases

When To Get Tested?

When you have had one or more unexplained blood clots (thrombotic episodes) in a vein or artery; when you have had recurrent miscarriages, especially in the second and third trimesters; when you have symptoms consistent with an autoimmune disease

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?


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Testing.com is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”

For more information, please read the article Reference Ranges and What They Mean.

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.

Common Questions

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.

View Sources

Sources Used in Current Review

Berg, T. (Updated 2015 April 15). Antiphospholipid syndrome and pregnancy. Medscape. Available online at http://emedicine.medscape.com/article/261691-overview. Accessed 12/27/2016.

(Reviewed 2016 March 21). Antiphospholipid syndrome. Lupus Foundation of America. Available online at http://www.lupus.org/answers/entry/antiphospholipid-syndrome. Accessed 12/27/2016.

Movva, S. (Updated 2016 July 1). Antiphospholipid syndrome workup. Medscape. Available online at http://emedicine.medscape.com/article/333221-workup. Accessed 12/27/2016.

Moake, J. (Revised 2016 September) Antiphospholipid antibody syndrome. Merck Manual Professional Version. Available online at http://www.merckmanuals.com/professional/hematology-and-oncology/thrombotic-disorders/antiphospholipid-antibody-syndrome-aps. Accessed 12/27/2016.

(Updated 2016 December). Antiphospholipid syndrome – APS. ARUP. Available online at http://www.arupconsult.com/Topics/APS.html?client_ID=LTD. Accessed 12/27/2016.

(© 2016) Antiphospholipid antibodies. The Johns Hopkins Lupus Center. Available online at https://www.hopkinslupus.org/lupus-tests/antiphospholipid-antibodies/. Accessed 12/27/2016.

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(May 17, 2012) National Heart, Lung and Blood Institute. How Is Antiphospholipid Antibody Syndrome Diagnosed? Available online at https://www.nhlbi.nih.gov/health/health-topics/topics/aps/diagnosis. Accessed January 2017.

Sources Used in Previous Reviews

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(2001 June 26). Antiphospholipid Antibody Syndrome. Hematology Resource Page, Patient Resources University of Illinois – Urbana/Champaign, Carle Cancer Center. Available online at http://www-admin.med.uiuc.edu/hematology/PtAPS.htm.

(© 2004). Antiphospholipid Testing. ARUP’s Guide to Clinical Laboratory Testing. Available online at http://www.arup-lab.com/guides/clt/tests/clt_al67.jsp#3965115.

Petri, M. (2001). Antiphospholipid Antibodies: Anticardiolipin Antibodies and the Lupus Anticoagulant in Systemic Lupus Erythematosus. The Lupus Foundation of America. Available online at http://www.lupus.org/education/brochures/antiphos02.html.

(© 2004). Cardiolipin Antibodies, IgG and IgM. ARUP’s Guide to Clinical Laboratory Testing. Available online at http://www.arup-lab.com/guides/clt/tests/clt_a133.jsp#1059158.

The Thrombophilias and Pregnancy. March of Dimes, Professionals and Researchers, Quick References and Fact Sheets. Available online at http://www.marchofdimes.com/professionals/681_9264.asp.

(2003 September, Modified) Anticardiolipin antibodies (IgG, IgM, IgA). Clinical Coagulation Laboratory Coagulation Test Descriptions. Available online at http://pathology.mc.duke.edu/coag/TestDes.htm.

Carsons, S. et. al. (2004 August 18, Updated). Antiphospholipid Syndrome. EMedicine. Available online at http://www.emedicine.com/med/topic2923.htm.

Arnout J.IS TH Scientic Standardisation Subcommittee Lupus Anticoagulants/Phospholipid dependent antibodies. International Society of Thrombosis and Haemostasis. Boston. July 2002.

Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 70-71.

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(2006 October 15, Revised). Antiphospholipid Antibody Syndrome. APS Foundation of America. Available online at http://www.apsfa.org/aps.htm. Accessed on 4/20/08.

(2008 February 5, Reviewed). Learning About Antiphospholipid Syndrome (APS). National Human Genome Research Institute. Available online at http://www.genome.gov/17516396. Accessed on 4/20/08.

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