Lupus Anticoagulant: Purpose of the Antibody Blood Test

The test confirms signs of blood clotting

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Lupus anticoagulant (LA) is an antiphospholipid antibody (APA) found in many people with lupus. LA makes your blood clot more—sometimes to a dangerous degree. Having this antibody gives you a greater risk of blood clots

Antibodies are cells in the immune system that target and destroy things that make you sick, like viruses and bacteria. Autoantibodies (antibodies to the self) are directed at things in your body.

An LA test is part of diagnosing antiphospholipid syndrome (APS), which is a potentially dangerous blood clotting disorder that's common in people with lupus and other connective tissue diseases. It can also occur—but much less often—in other people.

Blood clotting under a microscope
STEVE GSCHMEISSNER / Getty Images

What Is Lupus?

Lupus is a group of chronic autoimmune diseases that are unpredictable and 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).

Antiphospholipid Antibodies

Antiphospholipid antibodies seek out and attack:

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

These interfere 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.

The name lupus anticoagulant is misleading because it suggests LA increases bleeding, when it actually makes it clot. Also, it's 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:

  • Phenothiazines
  • Phenytoin
  • Hydralazine
  • Quinine
  • Amoxicillin

Symptoms

If you have 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 in an arm or leg
  • Increased risk of cardiovascular disease
  • Increased risk of pre-eclampsia and miscarriage

This antibody is dangerous, causing blood clots in about half of people with lupus and LA during a twenty-year period of time.

Lupus Anticoagulant Test

The lupus anticoagulant test 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'll actually slow the clotting time.

With or Without Lupus

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.

Preventing Blood Clots

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

With the right therapy, you can manage complications from LA.

There are some things you can do to prevent blood clots if you have LA:

  • Avoid estrogen-based birth control pills and hormone treatments for menopause
  • Don't smoke or use other tobacco products
  • Don't sit or lie down for extended periods other than when you're asleep
  • When traveling, get up periodically to keep your blood flowing
  • Move your ankles up and down when you can't move around

If you are 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. 

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, testing positive for lupus anticoagulant doesn't mean you're going to die from it. However, it is possible to die from a blood clot, so proper treatment and prevention are important.

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8 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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