What is the best definition of lupus anticoagulant?

Definition of Lupus Anticoagulant

Lupus anticoagulant is an antibody that reacts with phospholipids in the reagents for hemostasis tests, causing prolongation of the tests. 1, 2

Characteristics of Lupus Anticoagulant

Lupus anticoagulant (LA) is part of the antiphospholipid antibody family and has several key features:

• It consists of immunoglobulins (IgG, IgM, or both) that interfere with phospholipid-dependent coagulation tests 2
• Despite its name suggesting anticoagulation, LA is paradoxically associated with thrombotic events rather than bleeding 2, 3
• LA prolongs one or more in vitro phospholipid-dependent tests of coagulation, including:
  • Activated Partial Thromboplastin Time (APTT)
  • Dilute Russell's Viper Venom Time (dRVVT)
  • Kaolin Clotting Time (KCT)
  • Textarin Time (TT) 2

Laboratory Detection

The International Society on Thrombosis and Haemostasis recommends using two parallel tests for LA detection:

1. dRVVT (highest specificity for detecting LA in high-risk thrombosis patients)
2. LA-sensitive APTT with silica as activator 1

The diagnostic process follows a specific algorithm:

• Careful preparation of platelet-poor plasma is essential
• At least two screening tests must be performed
• Mixing studies are conducted to identify the presence of an inhibitor
• Confirmatory procedures demonstrate phospholipid-dependence of the inhibitor 2, 4

Clinical Significance

Understanding LA is critical because:

• Approximately 1/3 of individuals with LA experience thromboembolic complications (stroke, deep vein thrombosis, pulmonary emboli) 2
• LA is more strongly associated with thrombosis than other anticardiolipin antibodies 5
• LA can form immune complexes with prothrombin and phospholipids that may augment thrombin production, potentially explaining the thrombotic tendency 3
• LA testing is recommended in patients with antiphospholipid syndrome, particularly in young patients (<50 years) with unprovoked venous or arterial thrombosis, and in women with recurrent pregnancy loss 1

Common Pitfalls in LA Testing

• Not all APTT reagents have equal sensitivity to LA 1, 5
• Anticoagulant medications can interfere with test results 1
• Timing of testing is crucial - should be avoided during acute thrombosis or pregnancy 1
• Many laboratories still rely on poorly responsive screening assays, leading to misdiagnosis of weakly positive LA samples 5
• A single positive result is insufficient; confirmation requires repeat testing after >12 weeks 1

The definition that best describes lupus anticoagulant is therefore option B: an antibody that reacts with phospholipids in the reagents for hemostasis tests, causing prolongation of the tests.