Lupus Anticoagulant Antibody Blood Test

A positive result means greater risk of blood clots

Lupus anticoagulant (LA) is an antiphospholipid antibody (APA) that increases your risk of developing blood clots. It's found in many people with the autoimmune disease lupus and the related condition antiphospholipid syndrome.

Antibodies are specialized cells in the immune system that attack and destroy pathogens like viruses and bacteria. LA is an autoantibody, meaning it mistakes a healthy substance in your body for a pathogen.

As an antiphospholipid antibody, LA attacks phospholipids, which are an essential part of cell membranes.

This article looks at what LA does in your body, who's most likely to have it, how the test works, the symptoms of LA, and how to prevent blood clots.

Blood clotting under a microscope

What Is Lupus?

Lupus is a group of unpredictable chronic autoimmune diseases that can strike any part of your body. It most often involves inflammation of the skin, connective tissues, joints, kidneys, and heart. The most common form is systemic lupus erythematosus (SLE).

What Is Antiphospholipid Syndrome?

In antiphospholipid syndrome (APS), lupus anticoagulant seeks out and attacks:

  • Cell membrane components called phospholipids
  • Certain blood proteins that bind with phospholipids
  • Complexes that are formed when proteins and phospholipids bind

This interferes with the normal function of blood vessels and can lead to narrowed blood vessels or blood clots. That may lead to stroke, heart attack, and miscarriage.

Misleading Name

The name lupus anticoagulant is misleading because it suggests LA increases bleeding, when it actually makes it clot. It can also be present in people who don't have lupus.

Who Has Lupus Anticoagulant?

Lupus anticoagulant is not exclusive to lupus. But researchers who discovered it in the 1940s didn't know that.

Today, healthcare providers know it also occurs in people who have:

  • Other autoimmune diseases (such as inflammatory bowel disease)
  • Certain infections
  • Some tumors

It's also possible in people who take certain medications, including:

You don't need to have lupus to have APAs in your blood. About 2% of the total population tests positive for them. About 50% of people with lupus have them.

Lupus Anticoagulant Test

The lupus anticoagulant test is a blood test that detects LA antibodies. It doesn't test for lupus itself but looks at how fast your blood clots. Abnormal results may point to LA and antiphospholipid syndrome.

Coagulation tests, which measure how long it takes blood to clot, are used to detect LA. The first test is usually the activated partial thromboplastin time (aPTT). 

If the results of the aPTT are normal, they'll often use more sensitive tests to be sure. This may include:

  • Modified Russell viper venom test (RVVT)
  • Platelet neutralization procedure (PNP)
  • Kaolin clotting time (KCT)

While LA makes your blood clot faster in your body, in tests, it will actually slow the clotting time.

Why LA Tests Are Ordered

Your healthcare provider may order an LA test if you've had:

  • An unexplained blood clot
  • A lupus diagnosis and possible blood clot symptoms
  • Recurrent miscarriages
  • Other blood tests that show a slow clotting time

What the Results Mean

Normal results from clotting tests are 20–39 grams per liter (GPL) or micropulse lidar (MPL) units.

If your test is higher, your healthcare provider will likely re-test you in a few weeks to confirm the results before giving you a diagnosis of APS.

When to Call a Healthcare Provider

If you've tested positive for LA, you should be especially aware of the signs and symptoms of a blood clot, including:

  • Leg swelling or redness
  • Shortness of breath
  • Pain, numbness, and pallor (lack of color) in an arm or leg

You should also be aware of the signs and symptoms of cardiovascular disease and, if you're pregnant, the signs and symptoms of preeclampsia and miscarriage, as LA increases your risk of these problems.

Preventing Blood Clots

People who test positive for LA are often prescribed blood thinners to help prevent clots, but only when there's evidence of abnormal clotting. Steroids may be prescribed to assist in lowering antibody levels.

With the right therapy, you can manage complications from LA. To prevent blood clots:

If you're concerned about blood clots, speak to your healthcare provider about LA and your personal risk of developing blood clots. Your healthcare provider may have recommendations, specific to you, which can help lower your risk. 


Lupus anticoagulant is an autoantibody that attacks phospholipids, which are an important part of cell membranes. It causes problems with excessive blood clotting that can lead to stroke, heart attack, and miscarriage.

LA is most often found in people with lupus, but it can also be present in certain conditions and people who take certain medications. Coagulation blood tests are used to detect it.

Your healthcare provider may order LA tests if you've had a blood clot or symptoms or other possible problems associated with LA.

If you test positive for LA, you should be aware of the signs of blood clots and get medical help right away if you notice them. Talk to your healthcare provider about how to prevent blood clots.

Frequently Asked Questions

  • What does it mean to be lupus anticoagulant positive?

    It means you have autoantibodies in your blood that affect how your blood clots. This may mean you have antiphospholipid syndrome. It doesn't necessarily mean you have lupus.

  • What is the difference between lupus and lupus anticoagulant?

    Lupus is an autoimmune disease. Lupus anticoagulant is an autoantibody in the blood that indicates a clotting disorder. About half the people who test positive for lupus anticoagulant don't have lupus.

  • Is lupus anticoagulant fatal?

    No. However, it is possible to die from a blood clot, which LA puts you at greater risk of having.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Lupus Foundation of America. What is lupus?

  3. Fei X, Wang H, Jiang L, Zhao T, Cheng M, Yuan W. Clinical and prognostic significance of lupus anticoagulant measurement in patients with lung cancer. Technol Cancer Res Treat. 2017;:1533034617714150.  doi:10.1177/1533034617714150

  4. Duarte-García A, Pham MM, Crowson CS, et al. The epidemiology of antiphospholipid syndrome: A population-based study [published correction appears in Arthritis Rheumatol. 2020 Apr;72(4):597]. Arthritis Rheumatol. 2019;71(9):1545-1552. doi:10.1002/art.40901

  5. Laboratory Corporation of America: LabCorp. Lupus anticoagulant testing.

  6. Saint Luke's. Lupus anticoagulant.

  7. Lupus Foundation of America. Antiphospholipid antibodies syndrome.

  8. National Institutes of Health, U.S. National Library of Medicine: MedlinePlus. Lupus anticoagulants and antiphospholipid antibodies.

  9. National Institutes of Health, National Heart, Lung, and Blood Institute. Antiphospholipid antibody syndrome.

  10. Yale University: YaleMedicine. Blood clots in veins, heart and lungs.

By Jeri Jewett-Tennant, MPH
Jeri Jewett-Tennant, MPH, is a medical writer and program development manager at the Center for Reducing Health Disparities.