Antiphospholipid Syndrome Testing: Clotting + Miscarriage Workup
Content last reviewed 2026-09-12 · Educational information — not medical advice
Quick answer
APS testing hunts three antibodies (lupus anticoagulant, anticardiolipin, beta-2 glycoprotein I) in patients with unexplained clots, pregnancy losses, or thrombocytopenia. Diagnosis requires TWO positive tests 12+ weeks apart — transient positives from infection or inflammation don't count.
The triple antibody panel
- Lupus anticoagulant (functional clotting assay — paradoxically causes in-vitro prolongation despite IN-VIVO clotting)
- Anticardiolipin antibodies (IgG/IgM)
- Anti-beta-2 glycoprotein I antibodies (IgG/IgM)
Clinical criteria triggering testing
- Vascular thrombosis: any venous/arterial/small-vessel clot, unprovoked or at unusual site
- Pregnancy morbidity: ≥3 early losses <10 weeks, ≥1 fetal loss ≥10 weeks, or preterm delivery due to severe pre-eclampsia/placental insufficiency
- Thrombocytopenia, livedo reticularis, prolonged aPTT incidentally discovered
The 12-week persistence rule
Transient antibody positivity occurs with infections, medications, and normal aging — single-positive results mislead constantly. Formal APS diagnosis requires moderate-to-high-titer positivity CONFIRMED ≥12 weeks apart. This rule saves countless people from unwarranted lifelong anticoagulation.
Catastrophic APS
Rare (<1% of APS) but life-threatening: rapid multi-organ thrombosis from microvascular occlusion. CAPS registries track trigger identification (infection/surgery/pregnancy) and aggressive triple-therapy protocols (anticoagulation + steroids + plasma exchange).
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Frequently asked questions
What does lupus anticoagulant test if I'm already on warfarin?
Warfarin interferes with LA testing — specialized mixing studies or DOAC-specific assays needed; inform laboratory of anticoagulant status.
Positive APS with negative standard clotting tests — possible?
LA testing requires specialized clotting assays, not routine PT/PTT — negative standard tests don't rule it out.