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At a Glance

Why Get Tested?

To help investigate the presence of blood clots or an unexpectedly prolonged PTT (partial thromboplastin time), especially if you have had recurrent miscarriages; as part of an evaluation for antiphospholipid syndrome (APS); sometimes to help diagnose or evaluate an autoimmune disorder

When To Get Tested?

When you have an unexplained prolonged PTT test; when you have had recurrent unexplained blood clots; when you have had recurrent miscarriages, especially in the second and third trimesters

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?


You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”

For more information, please read the article Reference Ranges and What They Mean.

What is being tested?

Antiphospholipid antibodies are a group of immune proteins (antibodies) that the body mistakenly produces against itself in an autoimmune response to phospholipids. Tests can detect these autoantibodies that bind to phospholipids and, in a way that is not well understood, increase the risk of excessive blood clotting.

Several tests are available, including:

Phospholipids are structural components of cell membranes and play a crucial role in blood clotting. Phospholipds are critical to platelet function in addition to various coagulation co-factors. When antiphospholipid antibodies are produced, they interfere with the clotting process. They increase an affected person’s risk of developing recurrent inappropriate blood clots (thrombi) in arteries and veins, which can lead to strokes, heart attacks, and/or miscarriages.

Antiphospholipid antibodies are also associated with low platelet counts (thrombocytopenia) and with the risk of recurrent miscarriages (especially in the second and third trimester), premature labor, and pre-eclampsia.

One or more antiphospholipid antibodies have been identified in various conditions. Some examples are:

Autoimmune disorders



Use of certain drugs

  • Procainamide
  • Phenothiazines
  • Oral contraceptives

The presence of phospholipid antibodies in some instances may be temporary and they have been identified in some individuals who have no detectable illnesses.

Antiphospholipid syndrome (APS), also called Hughes syndrome, is a recognized group of signs and symptoms that includes the formation of blood clots, miscarriages, platelet deficiency (thrombocytopenia), and the presence of one or more antiphospholipid antibodies. APS can be primary with no underlying autoimmune disorder or secondary, existing with a diagnosed autoimmune disorder.

The 14th International Congress on Antiphospholipid Antibodies Task Force criteria for identifying APS requires testing for cardiolipin antibodies, lupus anticoagulant, and beta-2 glycoprotein antibodies when one of two clinical problems exist, blood clots (thrombosis) or pregnancy morbidity.


Common Questions

How is it used?

Antiphospholipid antibody testing is used to help determine the cause of:

  • Inappropriate blood clot formation (unexplained thrombotic episode, excessive clotting)
  • Recurrent miscarriage
  • Low platelet count (thrombocytopenia)
  • Prolonged PTT test

Depending on a person’s signs and symptoms and medical history, a healthcare practitioner may order one or more of these tests to help detect the presence of antiphospholipid antibodies and/or to help diagnose antiphospholipid syndrome (APS):

  • Cardiolipin antibodies (IgG, IgM, and sometimes IgA) are frequently ordered since they are the most common antiphospholipid antibodies.
  • Lupus anticoagulant assays (e.g., RVVT, LA-sensitive PTT) if a person has a prolonged PTT test.
  • Beta-2 glycoprotein 1 testing may be ordered along with the other antiphospholipid antibodies to detect their presence and to provide the healthcare practitioner with additional information.

If an antiphospholipid antibody is detected, the same test(s) may be repeated 12 weeks later to determine whether their presence is persistent or temporary.

Testing may also be performed to help diagnose and/or evaluate a person with an autoimmune disorder, which can occur along with disorders like lupus. If a person with an autoimmune disorder tests negative for antiphospholipid antibodies, testing may be repeated to determine if an antibody has developed in the course of the disease.

When is it ordered?

This testing may be ordered when a person has signs and symptoms suggestive of a blood clot (thrombotic episode), such as pain and swelling in the extremities, shortness of breath, and headaches. It also may be ordered when a woman has had recurrent miscarriages and/or as a follow-up to a prolonged PTT test.

When one of the tests is positive, it may be repeated several weeks later to determine whether the antibody is temporary or persistent. Antiphospholipid testing may be done when clinical signs suggest the presence of antiphospholipid syndrome.

When a person with a diagnosed autoimmune disorder tests negative for antiphospholipid antibodies, one or more of the tests may be repeated at regular intervals to screen for the development of an antiphospholipid antibody.

What does the test result mean?

Care must be taken when interpreting the results of antiphospholipid antibody tests. A negative result means only that the specific antibody tested was not present at the time of the test.

Low to moderate levels of one or more antibodies may occur temporarily due to an infection or drug or may appear as a person ages. These levels are often not considered significant but must be examined in conjunction with a person’s symptoms and other clinical information.

In some cases, a person may have one or more immunoglobulin classes of a specific antibody present or absent. For instance, the person may have significant quantities of IgG and IgM cardiolipin antibodies or may only be positive for the less frequently tested IgA cardiolipin antibody.

Moderate to high levels of one or more antiphospholipid antibodies, which persist when tested again 12 weeks later, indicate the likely continued presence of that specific antibody.

If tests indicate the presence of the lupus anticoagulant and it persists when retested, then it is likely that the person is positive for the lupus anticoagulant. People who have one or more antiphospholipid antibodies and those that are diagnosed with antiphospholipid syndrome can have an increased risk of having recurrent blood clots, recurrent miscarriages, and/or low platelets (thrombocytopenia).

Test results cannot predict the likelihood of complications, the type, or the severity in a particular person. Some people will have a variety of recurrent problems while others may never experience any difficulties. Examples of this include an asymptomatic individual who is diagnosed with antiphospholipid antibodies following a prolonged PTT test that is done for another reason (such as a pre-surgical screen) and an asymptomatic elderly person who has developed an antiphospholipid antibody.

Transient antiphospholipid antibodies may be seen in people who have inflammation, autoimmune disorders, infections, or cancer.

Is there anything else I should know?

Occasionally, antiphospholipid antibody testing may be ordered to help determine the cause of a positive VDRL/RPR test for syphilis. The reagents used to test for syphilis contain phospholipids and can cause a false-positive result in those with antiphospholipid antibodies.

False-positive test results may be seen in people who take drugs such as quinidine, procainamide, phenytoin, and penicillin.

Is there anything I can do to prevent or get rid of antiphospholipid antibodies?

No. The process by which these autoantibodies develop is not well understood. There are controllable risk factors, however, such as smoking and obesity that also increase your risk of clotting. Addressing these issues may help to lower your overall risk of developing blood clots but will not prevent the development of antiphospholipid antibodies or get rid of them once they are present.

If I have one antiphospholipid antibody, will I develop others?

It is possible, but there is no way to predict when or if this will happen. Antiphospholipid antibody development, and the development of symptoms and complications, varies by individual.

What is lupus anticoagulant?

Lupus anticoagulant (LA) is a type of antiphospholipid antibody that interferes with the clotting process in a test tube (so-called anticoagulant) but is associated with excessive clotting (venous or arterial thrombosis) in the body. There is no specific test for LA but is determined by performing a series of tests. For more details, see the article on Lupus Anticoagulant Testing.

Should everyone be tested for antiphospholipid antibodies?

General screening is not necessary. Testing is usually only performed if a person has associated signs or symptoms or as a follow up to other testing. Most people will never need to have this testing performed.

View Sources

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