What Is a Lupus Anticoagulant Test?

Medically Reviewed by Melinda Ratini, MS, DO on July 18, 2023
Written by WebMD Editorial Contributors
4 min read

Lupus anticoagulants cause clotting disorders that can lead to gangrene, miscarriages, strokes, and other problems. The lupus anticoagulant test measures the level of those antibodies in your body.

The lupus anticoagulant test is a blood test that checks for antibodies that cause a blood clotting disorder. Antibodies are proteins in your blood that fight off bacteria, viruses, and other germs. 

The name of this test is confusing because it doesn’t test for lupus. Lupus, also called systemic lupus erythematosus, is an autoimmune disease where your immune system attacks your tissues and causes inflammation. This disease can cause joint pain, rashes, and tiredness. 

A lupus anticoagulant test might also be called:‌

  • Lupus anticoagulant panel
  • Lupus inhibitor
  • Dilute russell viper venom test
  • Modified russell viper venom test
  • LA sensitive  

The term lupus anticoagulants is an inaccurate term. It was first coined when blood samples from lupus patients were tested and didn’t clot within a specific amount of time. But while lupus patients can have these antibodies, they aren’t only found in lupus and they aren’t only associated with bleeding.‌

Lupus anticoagulants belong to a group of antibodies called antiphospholipids. These are proteins that react to phospholipids, or fat molecules, in your blood cells and can stop your cells from working properly. ‌

Antiphospholipids can cause:‌

Other antiphospholipids that can also happen individually or alongside lupus anticoagulants, including:

  • Anticardiolipin antibody
  • Anti-beta 2 glycoprotein 1  
  • Anti-prothrombin
  • False-positive syphilis

About 50% of people who have lupus will have the lupus anticoagulant antibody. About half of these people will get a blood clot during their life.‌

People who don’t have lupus can also have this antibody, though. It’s thought that between 2% and 4% of people have it. It’s more common in older people, women, and during pregnancy. ‌

Your doctor will order this test if:‌

  • You have blood clots that can’t be explained.
  • You have lupus and have signs of blood clot.
  • A blood test shows your blood takes a long time to clot.
  • You have repeated miscarriages.‌

You can get lupus anticoagulants from other conditions.

Your doctor might also order a test if you have signs of a blood clot and have had any of the following:‌

  • Syphilis, a bacterial infection that's usually spread through sexual contact
  • Hepatitis C, a liver infection that is spread through the hepatitis C virus
  • Epstein-Barr virus, also called human herpesvirus 4, which can cause illnesses including mononucleosis (mono)
  • Oxidative stress, or damage caused by free radicals
  • Surgery
  • Certain medications‌

These conditions and medications are thought to expose the fat molecules in your cells, which allow the antibodies to attach and cause a blood clot.

The lupus anticoagulant is a simple blood test. You will go to the lab where they will take some of your blood with a needle. You might feel a sting and some minor discomfort, but it will pass quickly.

Lupus anticoagulant test results vary according to your age, health, gender, the method used, and other factors. 

If your lupus anticoagulant test is positive, this means you have antibodies in your blood. The test will also measure whether they are within the normal range. Normal results can vary from lab to lab, but a normal range is from 20 to 39 grams per liter (GPL) or micropulse lidar (MPL) units. ‌

If you have antibodies and they are higher than the normal amount, your doctor will want to repeat the test in a few weeks to confirm the results. They might also want to do other tests. ‌

If you take anticoagulant medications or herbs and vitamins that act like blood thinners, these can affect your results. Your doctor might have you get blood drawn before you start taking them. ‌

Infection and cancer can also affect your results.

If your test comes back positive and out of the normal range, your doctor will likely order other tests.

These can include:‌

  • Complete blood count, or CBC, which measures the number of red blood cells, white blood cells, and platelets in your blood
  • Anticardiolipin antibody, which measures whether this antibody is also in your blood
  • Activated partial thromboplastin time, which measures proteins called clotting factors and how long it takes your blood to clot
  • Kaolin clotting time, or KCT, also measures how long it takes your blood to clot
  • Coagulation factor assays, which check how your clotting factors are working
  • Platelet neutralization procedure, or PNP, which measures clotting time compared to activated partial thromboplastin time

Lupus anticoagulants aren’t found with just one type of test. Lab practices and different normal ranges can also affect your results. If a lupus anticoagulant test comes back positive, your doctor might ask you to do others.