From the Guidelines
The aPTT lupus sensitive (LA screen) should be interpreted with caution in patients taking anticoagulants, and the most recent guidance from the ISTH-SSC subcommittee on lupus anticoagulant/antiphospholipid antibodies recommends using strategies to circumvent interference from anticoagulation, such as removing anti-Xa or anti-IIa direct oral anticoagulant (DOAC) or using alternative tests like TSVT/ET 1.
Key Considerations
- The aPTT lupus sensitive (LA screen) is a blood test used to detect the presence of lupus anticoagulant, an antibody that can increase the risk of blood clots despite its name suggesting otherwise.
- This test is recommended for patients with unexplained thrombosis, recurrent pregnancy loss, or those suspected of having antiphospholipid syndrome.
- The test works by measuring how long it takes for blood to clot in a test tube containing phospholipids that are particularly sensitive to lupus anticoagulant.
- A prolonged clotting time compared to normal control plasma suggests the presence of lupus anticoagulant.
- However, this is considered a screening test, and positive results typically require confirmation with additional tests like the dilute Russell viper venom time (dRVVT) or mixing studies.
Interference from Anticoagulation
- False positives can occur in patients taking anticoagulants like heparin or warfarin, so medication history should be considered when interpreting results.
- The use of DOAC removal agents or alternative tests like TSVT/ET can help minimize interference from anticoagulation 1.
- Sampling during the trough period of low-molecular-weight heparin (LMWH) or DOAC is an alternative approach 1.
Clinical Implications
- The presence of lupus anticoagulant doesn't necessarily mean a patient has lupus; it's found in various autoimmune conditions and sometimes in otherwise healthy individuals.
- Positive results should be confirmed on repeat testing, and the time frame for retesting is no less than 12 weeks, based on expert opinion 1.
- Retesting of an equivocal result should be performed to confirm positivity or negativity, and low positive results around the cutoff value of aCL and aβ2GPI should be interpreted with care 1.
From the Research
aPTT and Lupus Anticoagulant
- The activated partial thromboplastin time (aPTT) is a test used to evaluate the intrinsic and common coagulation pathways in the blood 2.
- Lupus anticoagulant is an autoantibody that can cause aPTT prolongation and is associated with an increased risk of thrombosis [(2,3)].
- In some cases, lupus anticoagulant can cause bleeding tendency, especially when combined with other hemostasis abnormalities 2.
Diagnosis and Treatment
- Mixing studies can be used to diagnose the presence of lupus anticoagulant, and the index of circulating anticoagulant (ICA) can be used to predict its presence 3.
- Treatment with immunosuppressants, such as prednisolone, can correct aPTT values and resolve bleeding tendency 2.
- Anticoagulation therapy, such as vitamin K antagonists, can be used to treat patients with lupus anticoagulant and chronic atrial fibrillation 2.
Laboratory Testing
- The aPTT test can be influenced by various factors, including heparin, lupus anticoagulant, and clotting factors 4.
- Laboratories should establish and verify normal reference intervals for aPTT testing and assess the sensitivity of aPTT reagents to heparin, lupus anticoagulant, and clotting factors 4.
- Tissue thromboplastin inhibition test (TTIT) is a screening assay for detecting circulating anticoagulants, but its results can be influenced by the presence of unfractionated heparin (UFH) and low-molecular-weight heparins (LMWHs) 5.