At a glance
Also known as
LA; Lupus inhibitor; LAC
Why get tested?
To help evaluate a prolonged activated partial thromboplastin time (APTT) and/or a , to help determine the cause of recurrent fetal loss, as part of an evaluation for antiphospholipid syndrome. Not a diagnostic test for systemic lupus erythematosus (lupus).
When to get tested?
When you have a prolonged APTT test. When you have had a venous or arterial . 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.
What is being tested?
Lupus anticoagulant is a 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 fetal 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), 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 . 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-beta-2 glycoprotein 1 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.
Common Questions
Is sample collection really critical for lupus testing?
Yes. Besides heparin contamination, other pretest variables may have a significant impact on detecting the lupus anticoagulant. The blood sample is collected in a special citrated tube and centrifuged to remove the plasma (liquid part) for testing. There must be the proper amount of blood in the tube and it cannot be clotted. When the blood is centrifuged most of the platelets are left behind. If there are too many in the plasma sample, it may be compromised (because platelets are a source of phospholipids). Also, if the patient’s haematocrit (the amount of solid components in their blood) is elevated or decreased test results may be affected.
How is a lupus anticoagulant treated?
No treatment is required if someone does not have any symptoms. If blood clots do occur, patients are usually anticoagulated with heparin (which is injected under the skin or given intravenously (IV)) followed by oral warfarin (coumadin) therapy for several months. Higher than normal doses of warfarin may be required in this situation and the treatment may need to be continued for a longer period of time than normal. In someone with the lupus anticoagulant the risk of recurrence of both arterial and venous thrombotic episodes is relatively high. Some patients may need to be on long-term (even life-long) oral anticoagulation.
Which is more common anticardiolipin antibodies or LA?
In general, anticardiolipin antibodies are more common than the lupus anticoagulant. Anticardiolipin antibodies occur approximately five times more often than the lupus anticoagulant in patients with the antiphospholipid antibody syndrome. About sixty percent of those with the lupus anticoagulant will also have anticardiolipin antibodies.