Lupus Anticoagulant

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Also known as: LA; Lupus Inhibitor
Formal name: Lupus Anticoagulant
Related tests: Activated Partial Thromboplastin Time (aPTT), LA Sensitive aPTT (LA-aPTT), Thrombin Time, Autoimmune Diseases, Dilute or Modified Russell Viper Venom Time (dRVVT or MRVVT), Anticardiolipin Antibodies, Antiphospholipid Antibodies, Prothrombin Time (PT)

At a Glance

Why Get Tested?

To help evaluate a prolonged activated partial thromboplastin time (aPTT) and/or a thrombotic episode, to help determine the cause of recurrent fetal loss, as part of an evaluation for antiphospholipid syndrome. Not a diagnostic test for lupus (SLE).

When to Get Tested?

When you have a prolonged aPTT test. When you have had a venous or arterial thromboembolism. When you have had recurrent miscarriages, especially in the 2nd and 3rd trimesters.

Sample Required?

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

Test Preparation Needed?

None

The Test Sample

What is being tested?

Lupus anticoagulant is a protein that increases the risk of developing blood clots in both the veins and arteries. These clots may block blood flow in any part of the body, leading to strokes, heart attacks, pulmonary embolisms, deep vein thrombosis, and to recurrent foetal loss, especially in the 2nd and 3rd trimesters (thought to be related to clotting in placental blood vessels). The lupus anticoagulant is an acquired, not inherited, condition. Although it is found most frequently in those with autoimmune diseases, such as Systemic Lupus Erythematosus (SLE) and HIV, the lupus anticoagulant may also be seen chronically or temporarily in those with infections or cancers and in those who are taking certain medications, such as phenothiazines, chlorpromazine, procainamide, and fansidar. It is thought to be present in about 1 – 2% of the general population, and may develop in people with no known risk factors.
The term lupus anticoagulant (LA) is misleading. It is not a diagnostic test for lupus but gets its name because it was first discovered in patients with SLE, and because it often prolongs the activated partial thromboplastin time (aPTT) test - a timed blood test usually associated with anticoagulation and bleeding, not with thrombosis. It prolongs the aPTT test, as well as several other related tests, because the lupus anticoagulant binds to phospholipids and the reagents (chemicals) used in performing the aPTT test contain phospholipids.

In the body phospholipids play a vital role in the blood clotting process. They are found primarily on the surface of platelets and cell membranes and assist in the activation of several coagulation factors- proteins that are sequentially activated in response to blood vessel or tissue damage in a process called the coagulation cascade. The lupus anticoagulant is one of three types of test for antiphospholipid syndrome, associated with an increased risk of thrombosis. The others are anticardiolipin antibodies and antibodies against beta-2 glycoprotein 1 (less common). Any or all may be positive in antiphospholipid syndrome (also called Hughes' syndrome). Each interferes with the clotting process in a fashion that is not well understood and, singly or together, they increase a person's tendency to clot.

While anticardiolipin and anti-beta2-glycoprotein I antibodies may be tested for directly, there is not a single test for the lupus anticoagulant. It is usually diagnosed by using a panel of sequential tests that are taken through different stages. These tests operate on the principle that the lupus anticoagulant is a non-specific inhibitor – it does not target a specific coagulation factor, it binds to the assay’s phospholipids, inhibiting and prolonging the tests. The first test is usually an aPTT (or an LA-aPTT, a version of the test made more sensitive to LA) and the first stage is to see whether the original test is prolonged. If it is, then the patient’s plasma is mixed with pooled normal plasma (a combination of blood from different donors that contains all of the coagulation factors). If the prolongation is due to a specific coagulation factor deficiency then the normal plasma should "correct" the test to normal. If it is due to a non-specific inhibitor it will still be prolonged. In the third stage, additional phospholipids are added to the test. This should be sufficient to correct the test to near normal levels if the lupus anticoagulant is the cause of the abnormality. The Dilute Russell Viper Venom Test is a sensitive aPTT-like test for LA, and can also be performed with a phospholipid correction step.

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. However the blood sample has to be collected from a medium to large sized vein with minimal application of a tourniquet.

The Test

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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.