Also Known As
Formal Name
Antiphospholipid Antibodies
This article was last reviewed on
This article waslast modified on 16 August 2021.
At a Glance
Why Get Tested?

To help investigate inappropriate clot formation; to help determine the cause of recurrent miscarriage; to evaluate a prolonged PTT (partial thromboplastin time); as part of an evaluation for antiphospholipid antibody syndrome, as part of the evaluation of patients with connective tissue disease.

When To Get Tested?

When you have a prolonged PTT test; when you have had recurrent unexplained venous or arterial blood clots; when you have had recurrent miscarriages, especially in the second and third trimesters; if you have lupus or a related connective tissue disease.

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?


On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

Antiphospholipid antibody tests are immune proteins (antibodies) directed against phospholipids. Phospholipids are found in cell membranes including those of platelets. They are lipid molecules that play a crucial role in blood clotting. When antiphospholipid antibodies are produced, they interfere with the clotting process in a way that is not fully understood. They increase an affected patient’s risk of developing recurrent inappropriate blood clots (thrombi) in arteries and veins, which can lead to strokes and heart attacks. Antiphospholipid antibodies are also associated with thrombocytopenia (low platelets) and with the risk of recurrent miscarriages (especially in the 2nd and 3rd trimester), premature labour, and pre-eclampsia.

Antiphospholipid antibodies are frequently seen with autoimmune disorders such as Systemic Lupus Erythematosus (SLE). They may also be seen with HIV, some cancers, in the elderly and temporarily with infections and with some drug treatments (such as phenothiazines and procainamide).

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

The most common antiphospholipid antibodies are cardiolipin antibodies (also called anticardiolipin antibodies or ACA) and the lupus anticoagulant. Others tested include anti-beta2 glycoprotein I and anti-phosphatidylserine. There are two types of tests that are used to detect antiphospholipid antibodies. The first is the test for cardiolipin or beta2 glycoprotein I antibodies. The tests used can detect several classes (IgG, IgM, and/or IgA) of the antibodies themselves. The second type are lupus anticoagulant assays, which are functional tests that measure the time it takes for a patient’s sample to clot, and they require the presence and action of phosopholipids for clotting to occur. Lupus anticoagulant assays begin with an assay to detect prolongation of clotting, the most common of which is the PTT. Confirmatory studies then need to be performed, preferably with a similar method as the initial screening assay.

Additional diagnostic and confirmatory tests may include RVVT (Russell viper venom time), PNP (platelet neutralisation procedure), KCT (kaolin clotting time) and/or hexagonal lipid neutralisation test.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

Accordion Title
Common Questions
  • How is it used?

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

    Antiphospholipid antibody testing is used to help determine the cause of an unexplained thrombotic episode, recurrent pregnancy loss, thrombocytopenia, and/or a prolonged PTT test. Since the presence of both lupus anticoagulant and an antiphosphlipid antibody (anticardiolipin or B2GP1 antibody) has a higher specificity for the diagnosis of antiphospholipid syndrome, both tests should usually be performed at the same time.

    If an antiphospholipid antibody is detected, the same test(s) should be requested 12 to 24 weeks later to determine whether their presence is persistent or temporary. If a patient with an autoimmune disorder tests negative for antiphospholipid antibodies, they may be retested as these antibodies can develop at any time.

  • When is it requested?

    Antiphospholipid antibody testing may be requested when a patient has symptoms suggestive of a thrombotic (clotting) episode, such as pain and swelling in the extremities, shortness of breath, and headaches. It also may be requested 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 patient with an autoimmune disorder tests negative for antiphospholipid antibodies, one or more of the tests may be requested in the future 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 concentrations are often not considered significant but must be examined in conjunction with a patient’s symptoms and other clinical information. In some cases, a person may have one or more classes of a specific antibody present or absent. For instance, they may have significant quantities of IgG and IgM cardiolipin antibodies with or without Beta-2 GP1 antibodies. Moderate to high levels of one or more antiphospholipid antibodies, which persist when tested again 12 to 24 weeks later, indicate the likely continued presence of that specific antibody.

    If the tests indicate the presence of the lupus anticoagulant and it persists when retested, then it is likely that the patient is positive for the lupus anticoagulant. Patients who are diagnosed with antiphospholipid syndrome have an increased risk of having recurrent thrombotic episodes, recurrent miscarriages, and thrombocytopenia. Test results cannot predict, however, the likelihood of complications, the type, or the severity in a particular patient. Some will have a variety of recurrent problems while others may never experience any difficulties. Examples of this include an asymptomatic patient who is found to have antiphospholipid antibodies following a prolonged PTT test that is done for another reason (such as a pre-surgical screen), or an asymptomatic older person who has acquired an antiphospholipid antibody.

  • Is there anything else I should know?

    Occasionally, antiphospholipid testing may be requested 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 patients with antiphospholipid antibodies.

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

    No. The process that causes them to be produced 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 thrombi.

  • 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 and it is just as likely that if they are low level antibodies that they will disappear. Antiphospholipid antibody development, and the development of symptoms and complications, depends on the individual.