Lupus Anticoagulant Antibody Blood Test

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.

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.

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:

• Phenothiazines
• Dilantin (phenytoin)
• Hydralazine
• Qualaquin (quinine)
• Amoxicillin
  

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:

• 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'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. 

Summary

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.