What is LA, LAC ?
Lupus anticoagulants or LAs are autoantibodies targeted against the body’s own cells. They trigger an autoimmune response in the body and increase the risk of development of blood clots. Lupus Anticoagulant Tests are a series of tests performed to detect the presence or absence of lupus anticoagulants in blood.
Why is LA, LAC done?
The Lupus Anticoagulant Test is performed:
· To determine the cause of formation of abnormal blood clots inside blood vessels
· To help determine the cause of repeated miscarriages
· As a part of panel of tests performed to evaluate antiphospholipid syndrome
What does LA, LAC Measure?
Lupus anticoagulants are antibodies produced against the body’s own cells. These are produced when the immune system mistakenly identifies the body’s own cells as foreign matter and are specifically targeted against phospholipids and related proteins on the cell membranes. As a result, lupus anticoagulants affect the blood clotting process (thrombosis) and increase the risk of formation of blood clots.
The name lupus anticoagulant is a misnomer.
a) Despite being called ‘Lupus’, these autoantibodies are not related to the autoimmune condition systemic lupus erythematosus (SLE), commonly called lupus. They are called lupus anticoagulants because they were first observed in patients suffering from SLE. Lupus Anticoagulant Test is not used to diagnose SLE as these autoantibodies are commonly absent in patients of SLE, while they may be found in a number of other conditions.
b) They are called ‘anticoagulants’ even though they facilitate blood clot formation because lupus anticoagulants reduce blood clotting in laboratory tests performed to measure clotting like Partial Thromboplastin Time (PTT) Test. Lupus Anticoagulants do not cause bleeding by themselves.
Lupus Anticoagulant Test involves a series of tests performed sequentially to determine the presence of these autoantibodies. The first set measures clotting time with tests based on phospholipid reagents since these are targeted by LA. These include Partial Thromboplastin Time (PTT) Test, Lupus Anticoagulant sensitive Partial Thromboplastin Time (PTT-LA), and Dilute Russel Viper Venom Test (DRVVT). These tests measure the time taken for blood to clot (clotting time) in seconds, and the presence of lupus autoantibodies increases clotting time. Abnormal results in these tests are followed up with other tests that determine the capacity of the blood to clot, including:
· Mixing study, where equal volumes of the patient plasma sample and normal pooled plasma sample are mixed together, followed by PTT-LA and DRVVT on the mixture
· Correction or neutralization study, where excess phospholipids are added to the patient plasma sample, on which PTT-LA and DRVVT are performed
Presence of lupus anticoagulants in blood is associated with increased risk of thrombosis (formation of blood clots) in blood vessels, leading to an increased risk of heart attack, stroke, pulmonary embolism, as well as recurring miscarriage. LA is one of the three primary antiphospholipid antibodies, the other two being Cardiolipin antibody and β-2-glycoprotein antibody. Presence of these individually or together increases the chances of thrombosis and antiphospholipid antibody syndrome (APS). Thrombosis is more common in people with LA.
Lupus anticoagulants may sometimes be present without developing symptoms of abnormal clotting.
Interpreting LA, LAC results
PTT: 28.60 to 41.10 seconds
PTT-LA: 31.40 to 43.40 seconds
DRVVT: No LA present
Lupus Anticoagulant Tests are performed sequentially and results may be interpreted as follows:
PTT-LA and/or DRVVT
No further testing required. Repeat testing if inhibitor suspected strongly.
Inhibitor may be present.
To Step 2
Mixing Study: Equal parts patient plasma and normal pooled plasma followed by PTT-LA and DRVVT
Abnormal Step 1 result due to coagulation factor deficiency.
Lupus anticoagulant may be present.
To Step 3
Confirmation (Correction or Neutralization test): Excess phospholipids added to patient plasma followed by PTT-LA or DRVVT.
A ratio is calculated by dividing Step 3 result into Step 1 result.
Positive (high ratio)
Lupus anticoagulant present
Negative (low ratio)
Specific inhibitor other than lupus anticoagulant present.
Based on recommendations of the International Society of Thrombosis and Hemostasis (ISTH) presence of LA is confirmed if four specific criteria are met:
· Prolonged result in at least one of PTT-LA or DRVVT tests
· Prolonged result in mixing study
· Reduction of clotting time occurs upon addition of excess phospholipids
· Ruling out other specific inhibitors of coagulation factors like factor VIII
Answers to Patient Concerns & Frequently Asked Questions (FAQs) about LA, LAC
Frequently Asked Questions about Lupus Anticoagulant