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 form of antiphospholipid antibodies. They are acquired autoantibodies that can affect the body's ability to regulate blood clotting in a way that is not well understood.

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 an affected patient's risk of developing recurrent inappropriate blood clots (thrombi) in both arteries and veins. 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 be seen temporarily in patients with acute infections, HIV/AIDS, some cancers, with drug treatments (such as phenytoin, penicillin, and procainamide), and asymptomatically in the elderly.

They may occur in low titre, which has no known clinical significance.

When a patient has excessive blood clot 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 (50%) or secondary, existing with a diagnosed autoimmune disorder, most commonly SLE.

How is it used?

Tests for IgG and IgM cardiolipin antibodies are frequently ordered to help determine the cause of an unexplained thrombotic episode, recurrent miscarriage, or thrombocytopenia. They may be ordered along with lupus anticoagulant testing to help investigate the cause of a prolonged APTT (activated partial thromboplastin time), especially if clinical findings suggest that the patient may have SLE or another autoimmune disorder. If the primary test results are unremarkable but clinical suspicions still exist, then IgA cardiolipin antibody testing may be ordered.

If one or more of the classes of cardiolipin antibodies is detected, then the same test(s) are usually repeated at least 12 weeks apart to help determine whether their presence is persistent or temporary. Low to moderate levels of cardiolipin antibodies are often of no clinical significance. Titres of cardiolipin antibodies may fluctuate considerably over time, and this needs to be taken into account when testing.

If a patient 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.

When is it requested?

Cardiolipin antibody testing may be ordered when a patient has symptoms suggestive of a thrombotic episode, such as pain and swelling in the extremities, shortness of breath, or headaches. It 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 APTT test. When an IgG, IgM, and/or IgA cardiolipin antibody is detected, then it 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 ordered in the future to screen for their development.

What does the 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 emerging, temporarily due to an infection or drug, or asymptomatically as a person ages. The low to moderate concentrations of antibody seen in these situations are frequently not significant, but they must be examined in conjunction with a patient’s symptoms and other clinical information.

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

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 (chemicals) used to test for syphilis contain phospholipids and can cause a false positive result in patients with cardiolipin antibodies.

Common questions

• If I have anticardiolipin 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. Compared to the presence of lupus anticoagulant, cardiolipin antibodies are lesser risk factors for thrombosis.

• 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 plans around this risk factor.
 

More information

RCPA Manual: Cardiolipin antibodies