From the Guidelines
Lupus anticoagulant (LA) testing should be performed using a stepwise approach, starting with initial screening tests of activated partial thromboplastin time (aPTT) and dilute Russell's viper venom time (dRVVT), as recommended by the ISTH-SSC LA/aPL Subcommittee 1. This approach is supported by recent studies, including a 2025 update on laboratory detection and interpretation of antiphospholipid antibodies for diagnosis of antiphospholipid syndrome, which emphasizes the importance of using a combination of tests to detect LA 1. The stepwise approach includes:
- Initial screening tests: Perform aPTT and dRVVT
- Mixing studies: If screening tests are prolonged, perform 1:1 mixing studies with normal pooled plasma
- Confirmatory tests: Use phospholipid-dependent assays such as Staclot LA or platelet neutralization procedure
- Repeat testing: Positive results should be confirmed after 12 weeks to establish persistence Testing should be done when patients are not on anticoagulants, if possible, and results should be interpreted cautiously if anticoagulation cannot be stopped 1. The use of aPTT and dRVVT has been shown to have high LA detection rates and is widely used in most diagnostic laboratories 1. It is also important to note that the 12-week repeat testing is crucial because transient LA can occur during infections or with certain medications, and persistence of LA is a key criterion for diagnosing antiphospholipid syndrome 1.
From the Research
Guidelines for Testing Lupus Anticoagulant (LA)
The guidelines for testing Lupus Anticoagulant (LA) involve several steps and considerations, including:
- Screening tests, such as diluted Russell Viper Venom Time (dRVVT) and activated partial thromboplastin time (APTT), to detect the presence of LA 2, 3, 4
- Mixing studies to confirm the presence of LA and exclude other causes of prolonged clotting times 5, 4
- Confirmatory tests, such as phospholipid dependency tests, to verify the presence of LA 2, 3, 4
- Evaluation of the patient's clinical history and other laboratory test results, such as antiphospholipid antibodies, to support the diagnosis of antiphospholipid syndrome (APS) 3, 4, 6
Considerations for Testing
Several considerations must be taken into account when testing for LA, including:
- The potential for interference from other substances, such as heparin and vitamin K antagonists, which can affect the accuracy of the test results 2, 4
- The need to use multiple testing methods, such as dRVVT and APTT, to increase the sensitivity and specificity of the testing 3, 4
- The importance of following established guidelines and criteria for interpreting test results, such as those provided by the International Society for Thrombosis and Haemostasis (ISTH) 6
- The potential for variability in test results and the need for careful evaluation and correlation with clinical findings 3, 6
Testing Methods
Several testing methods are available for detecting LA, including: