Laboratory investigation of a LA should begin with screening assays including:
- Prothrombin time (PT)
- Activated partial thromboplastin time (aPTT)
- Thrombin time (TT)
Performing these tests will help to screen for a LA and provide information for additional testing that should be performed. Additionally, these screening tests can help to ensure the integrity of the patient sample. There is no specific testing for LA; however, the Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibody of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis have set up testing criteria:
- Prolongation of at least one phospholipid-dependent clotting test (usually assay with low phospholipid content).
- Evidence of inhibitory activity shown by the effect of patient plasma on pooled normal plasma (mixing studies).
- Evidence that the inhibitory activity depends on phospholipid. This may be achieved by addition or alteration of phospholipid, hexagonal phase phospholipid, platelets, or platelet vesicles in the test system.
- LAs must be carefully distinguished from other coagulopathies that may give similar laboratory results or may occur concurrently with LAs. Specific factor assays or the clinical history may be helpful in differentiation LAs from other possibilities.
- To exclude the presence of LA at least two different screening assays need to be negative.
- The presence of LA must be confirmed after at least 12 weeks, better after one year.