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Antiphospholipid Antibody

Does this test have other names?

APA, lupus anticoagulant, anticardiolipin antibodies

What is this test?

This blood test checks for antiphospholipid antibodies, which may be found in people with abnormal blood clots or autoimmune diseases.

Your immune system usually creates antibodies in response to an infection or a foreign invader like bacteria. Antiphospholipid antibodies are usually made when your immune system mistakes part of your own body for a harmful substance. In this case, the antibodies seem to be reacting to phospholipids, a normal part of your blood vessels.

People who have abnormal blood clots, repeated miscarriages, or autoimmune diseases like lupus and multiple sclerosis often have antiphospholipid antibodies. People with cancer may also have these antibodies, which often fade away when the cancer is treated.

The two most common types of antiphospholipid antibodies are lupus anticoagulant and anticardiolipin antibodies. Testing for lupus anticoagulant often uses a test like the Russell viper venom time (RVVT) or kaolin clotting time. RVVT measures how long it takes a type of viper venom to trigger a blood clot. Kaolin clotting time is used to diagnose clotting disorders and detect the lupus anticoagulant. Measuring anticardiolipin antibodies is done directly by looking for antibodies against the cardiolipin molecule.  

Why do I need this test?

You may need this test if you:

  • Have repeated miscarriages

  • Develop abnormal blood clots that could lead to heart attack or stroke

  • Have antiphospholipid antibody syndrome, a group of symptoms that includes miscarriages, a platelet deficiency, and abnormal blood clots

  • Have lupus or cancer

What other tests might I have along with this test?

Your doctor may also order a partial thromboplastin time, or PTT, which may help find out the cause of a blood clot or bleeding disorder. You may also have a dilute prothrombin test, which helps measure how long it takes a clot to form. 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

A negative result means that these antibodies are not present. Low to moderate results may mean the antibodies are present because of a recent health problem or a drug you have taken. High levels of this antibody may mean you have a higher risk for blood clots, but your doctor cannot predict when a clot may happen. Your doctor may order a second test in about 12 weeks to confirm the results.

A positive result does not necessarily mean you need medical treatment. If you have antiphospholipid syndrome, your doctor may suggest treatment that includes warfarin, an anti-clotting medication. Your health care provider will interpret the results in light of your overall health. 

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. 

What might affect my test results?

Certain tests for syphilis can cause a false-positive on this test if done at the same time. Your doctor may order a second test to confirm the results. Recent viral infections, such as HIV, can also skew the results.

How do I get ready for this test?

You don't need to prepare for this test.  But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.