Antiphospholipid Antibodies

Antiphospholipid testing is used to help determine the cause of an unexplained thrombotic episode, recurrent fetal loss, thrombocytopenia, and/or a prolonged PTT test. Depending on the patient’s clinical findings, a physician may order one or more types and classes of these tests to help detect the presence of antiphospholipid antibodies and to help diagnose antiphospholipid syndrome (APS). Cardiolipin antibodies (IgG, IgM, and sometimes IgA) are frequently ordered as they are the most common antiphospholipids. If a patient has a prolonged PTT test, further lupus anticoagulant testing is usually indicated. Anti-beta2 glycoprotein I and anti-phosphatidylserine testing may be ordered along with the other antiphospholipid antibodies to detect their presence and to provide the doctor with additional information.

If an antiphospholipid antibody is detected, the same test(s) may be ordered 8 to 10 weeks later to determine whether their presence is persistent or temporary. If a patient with an autoimmune disorder tests negative for antiphospholipid antibodies, he may be retested as these antibodies may develop at any time.

Antiphospholipid antibody testing may be ordered when a patient has symptoms suggestive of a 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 patient with an autoimmune disorder tests negative for antiphospholipid antibodies, one or more of the tests may be ordered in the future to screen for the development of an antiphospholipid antibody.

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 or they 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 8 to 10 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 have one or more antiphospholipid antibodies and those that 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 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 acquired an antiphospholipid antibody.

Occasionally, antiphospholipid 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 patients with antiphospholipid antibodies.