What Are Lupus Anticoagulants? Everything to Know

Medically Reviewed By Angelica Balingit, MD
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Lupus anticoagulant is a type of immunoglobulin or antibody. It can prolong the time it takes for blood to clot, increasing the risk of arterial or venous thrombosis. An estimated 2–4% of the general population have lupus anticoagulant present in their blood. The incidence increases to 15–34% among people with systemic lupus erythematosus (SLE).

This article explains what lupus anticoagulants are and what the lupus anticoagulant test involves. It also discusses who may need a lupus anticoagulant test and when to contact a doctor.

What are lupus anticoagulants?

There is a collection of vials.
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Lupus anticoagulants are a type of antiphospholipid antibody.

Ordinarily, an antibody is a protein that circulates in the blood to help protect the immune system from antigens. Antigens are foreign substances such as bacteria or viruses.

However, antiphospholipid antibodies work against proteins that bind phospholipids. The reason why the body creates antiphospholipid antibodies is unclear, although researchers believe that environmental factors, such as an infection, may trigger it.

Are lupus anticoagulants connected to lupus?

The name “lupus anticoagulant” is potentially misleading, as the antibodies are not only present in people with lupus. In fact, lupus anticoagulants are only present in about 15–34% of people with SLE.

Additionally, the term “anticoagulant” in the name may be misleading. Lupus anticoagulants increase your risk of blood clots rather than bleeding.

The term originally referred to a phenomenon in which plasma samples in people with SLE did not clot within the expected time.

It is possible that SLE may trigger the immune system to create antiphospholipids, such as lupus anticoagulants.

Learn more about SLE.

What is lupus anticoagulant syndrome?

Antiphospholipid syndrome — sometimes called lupus anticoagulant syndrome if it involves those antibodies — is a multisystemic autoimmune disorder. It occurs when there are persistent antiphospholipid antibodies alongside one of the following:

  • arterial thrombus
  • venous thrombus
  • pregnancy loss

Arterial and venous thrombus, or blood clots, most commonly affect the lower limbs and the cerebral arterial circulation. However, thrombosis can develop in any organ.

Alongside lupus anticoagulants, other types of antiphospholipid antibodies responsible for antiphospholipid syndrome include anticardiolipin antibodies IgG or IgM and anti-beta-2-glycoprotein-I antibodies IgG or IgM.

Learn more about antiphospholipid syndrome.

What is a lupus anticoagulant test?

A lupus anticoagulant test is a blood test. Doctors will take a sample of your blood and send it to a laboratory for a series of tests.

In particular, the test involves mixing the plasma sample with a reagent containing phospholipids and seeing how long it takes to clot. If it takes a long time for the sample to clot, this could indicate the presence of antiphospholipids such as lupus anticoagulants.

The laboratory may also run other tests at the same time to check for anticardiolipin and anti-beta-2-glycoprotein I antibodies. They can be responsible for antiphospholipid syndrome.

Learn more about blood tests.

When do I need a lupus anticoagulant test?

A doctor will recommend a lupus anticoagulant test if you frequently experience blood clots or if they suspect that you have antiphospholipid syndrome.

They may also recommend a lupus anticoagulant test if you have experienced multiple pregnancy losses, as antiphospholipid antibodies are a major cause of this and other complications in pregnancy.

However, it is important to note that there are other possible causes of pregnancy loss. Learn more about miscarriage.

Risk factors for blood clots

Certain factors make you more likely to develop a blood clot. These risk factors include:

  • having previously had a blood clot
  • being pregnant or having just had a baby
  • inflammatory conditions, such as rheumatoid arthritis or Crohn’s disease
  • having limited mobility, such as being unable to leave the bed at home or in the hospital
  • recent trauma
  • being overweight
  • smoking
  • using combined hormonal contraception, such as the contraceptive patch, combined pill, or vaginal ring

If you have concerns about blood clots, you should consult a doctor.

Learn more about blood clots.

What happens during a lupus anticoagulant test?

A blood test is a quick procedure that a doctor or nurse can carry out in their office.

They will insert a needle into your vein, usually in your arm. They will then draw a small amount of blood into the syringe or container attached to the needle.

As they only take a small amount of blood, you should not experience any serious side effects. However, some people do feel dizzy or faint during or after a blood test. It is important to let the doctor or nurse know if you feel unwell.

What do my lupus anticoagulant test results mean?

If the plasma sample in your blood takes longer than expected to clot, this may indicate that there are antiphospholipid antibodies in your blood. The laboratory will be able to test for these and confirm whether your blood contains lupus anticoagulants.

If your blood sample is positive for lupus anticoagulants, the doctor will be able to advise on the most suitable treatment options.

For example, if you experience thromboembolism, the doctor may recommend warfarin, which is a blood-thinning medication. If you are pregnant, they may recommend a blood thinner called heparin.

Make sure that you ask the doctor any questions you may have before beginning treatment.

When should I contact a doctor?

You should contact a doctor as soon as you have concerns about lupus anticoagulants. In particular, you should seek medical advice if you experience blood clots or recurrent pregnancy loss.

The doctor will recommend tests to aid diagnosis. It is also important to ask the doctor any questions you have about your symptoms and any tests they arrange for you.


Lupus anticoagulants are a type of antiphospholipid antibody that interferes with the time it takes for your blood to clot, increasing your risk of conditions such as thrombosis.

If your doctor suspects antiphospholipid syndrome, they will be able to arrange a lupus anticoagulant blood test. The laboratory will test the rate at which plasma samples from your blood clot. If clotting takes longer than expected, this can indicate that you have antiphospholipid antibodies in your blood.

It is important to contact your doctor if you have concerns about lupus anticoagulants or any known complications that the antibodies may cause. Your doctor will be able to arrange the necessary tests and advise on any treatments they recommend.

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Medical Reviewer: Angelica Balingit, MD
Last Review Date: 2022 Aug 11
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