From the Guidelines
The diagnosis of antiphospholipid antibody syndrome (APS) requires positive results on at least one of three main tests: lupus anticoagulant, anticardiolipin antibodies (IgG and/or IgM), or anti-beta2 glycoprotein I antibodies (IgG and/or IgM), with tests repeated at least 12 weeks apart to confirm persistence of antibodies 1. The laboratory tests for APS include:
- Lupus anticoagulant (LA)
- Anticardiolipin antibodies (aCL) of IgG and/or IgM isotype
- Anti-beta2 glycoprotein I antibodies (aβ2GPI) of IgG and/or IgM isotype These tests should be performed in specialized laboratories with experience in these assays, as standardization can vary 1. Additional supportive tests may include:
- Russell viper venom time (RVVT)
- Activated partial thromboplastin time (aPTT)
- Tests for other phospholipid antibodies It's essential to note that patients should avoid anticoagulant medications before testing when possible, as these can interfere with results, particularly for lupus anticoagulant 1. The persistence of antibodies over time is crucial for diagnosis because it distinguishes pathological antibodies from transient ones that may appear during illness but don't indicate true APS 1. The 2023 American College of Rheumatology (ACR)/European Alliance of Associations for Rheumatology (EULAR) classification criteria for APS define moderate and high titer thresholds as 40 and 80 Units, respectively, with cutoffs calculated by the 99th percentile abandoned 1. Concurrent testing for LA, aCL IgG and IgM, and aβ2GPI IgG and IgM is recommended, with measurement of LA in citrated plasma according to the ISTH-SSC recommendations 1.
From the Research
Antiphospholipid Antibody Syndrome Laboratory Tests
The laboratory tests for antiphospholipid antibody syndrome (APS) include:
- Lupus anticoagulant (LA) testing using clot-based assays 2, 3, 4, 5
- Solid-phase assays for anti-cardiolipin antibodies (aCL) and anti-β2 glycoprotein I antibodies (aβ2GPI) with immunoglobulin subclasses of IgG and/or IgM 2, 3, 4, 5, 6
Types of Assays
The assays used to detect antiphospholipid antibodies can be categorized into two types:
- Liquid-phase assays: used to identify lupus anticoagulant (LA) 3, 4, 5
- Solid-phase assays: used to detect anti-cardiolipin antibodies (aCL) and anti-β2 glycoprotein I antibodies (aβ2GPI) 2, 3, 4, 5, 6
Challenges in Laboratory Testing
The laboratory diagnosis of APS can be challenging due to: