Antiphospholipid Antibodies

Print this article
Share this page:
Also known as: APA
Formal name: Antiphospholipid Antibodies
Related tests: Lupus Anticoagulant Testing, Cardiolipin Antibodies, PTT (partial thromboplastin time), Platelet neutralisation procedure, Kaolin clotting time, Hexagonal phospholipid confirmatory test, Dilute prothrombin time, Anti-beta2 glycoprotein I antibodies, Anti-phosphatidylserine antibodies, Anti-prothrombin antibodies

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?


The Test Sample

What is being tested?

Antiphospholipid antibody tests are used to detect several specific binding proteins that the body produces against itself in an autoimmune response to phospholipids. Found in cell membranes and platelets, phospholipids are a normal part of the body. 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 preeclampsia.

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), 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 diagnosed autoimmune disorder).

The most common antiphospholipid antibodies are cardiolipin antibodies (also called anticardiolipin antibodies) 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.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

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

No test preparation is needed.

The Test

Common Questions

Ask a Laboratory Scientist

Article Sources

« Return to Related Pages

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.