Lupus Anticoagulant

Function

The Lupus Anticoagulant (LA) test is a functional assay used to detect specific autoantibodies that interfere with the phospholipid-dependent coagulation process. Despite its name, it is a pro-thrombotic factor, meaning it promotes blood clotting rather than preventing it. These antibodies belong to the antiphospholipid antibody family and are often found in patients with systemic lupus erythematosus (SLE) and other autoimmune conditions.

Why it is Ordered

Physicians typically order the LA test when a patient experiences unexplained blood clots (thrombosis), recurrent miscarriages, or a prolonged Activated Partial Thromboplastin Time (aPTT) that does not correct when mixed with normal plasma. It is a critical component in the diagnosis of Antiphospholipid Syndrome (APS), a condition characterized by both laboratory evidence of antibodies and clinical events like arterial or venous thrombosis.

Associated Conditions

• Antiphospholipid Syndrome (APS): The primary condition associated with persistent positive LA results.
• Systemic Lupus Erythematosus (SLE): Approximately 30% of SLE patients may test positive for LA.
• Thrombophilia: Increased risk for Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE).
• Obstetric Complications: Including pre-eclampsia and unexplained fetal loss.

Testing Procedure

Testing usually involves a multi-step process: a screening test (like the Dilute Russell Viper Venom Time - dRVVT), followed by a mixing study to exclude factor deficiencies, and finally a confirmation test adding excess phospholipids. A positive result is only clinically significant if it persists for more than 12 weeks.