Antiphospholipid syndrome (APS)
An autoimmune condition that makes the blood too likely to clot. It causes blood clots in veins or arteries and, in pregnancy, recurrent miscarriage — driven by antibodies that must be confirmed on two tests 12 weeks apart.
What it is
Antiphospholipid syndrome is an autoimmune disorder in which the immune system makes antibodies (antiphospholipid antibodies) that make the blood prone to clotting. It shows up as venous clots (such as deep vein thrombosis or pulmonary embolism), arterial clots (including stroke at a young age), or pregnancy problems — recurrent early miscarriage, or later pregnancy loss and complications. It can occur on its own (primary) or alongside another autoimmune disease, most often lupus. Diagnosis requires both a clinical event (a clot or defined pregnancy complication) and a persistently positive antibody test — the three antibodies are lupus anticoagulant, anticardiolipin and anti-beta-2-glycoprotein-I — confirmed on two occasions at least 12 weeks apart, because transient positives are common after infections. A confusing quirk is that the 'lupus anticoagulant' actually prolongs a clotting test (the APTT) in the lab while promoting clotting in the body.
Key lab markers
- Antiphospholipid antibodies — lupus anticoagulant, anticardiolipin, anti-beta-2-glycoprotein-I; the defining tests, confirmed twice 12+ weeks apart.
- APTT — may be prolonged by the lupus anticoagulant (paradoxically, despite a clotting tendency).
- Platelets — can be low.
- D-dimer — raised with acute clots.
- ANA and anti-dsDNA — checked because APS often coexists with lupus.
- Imaging — ultrasound or CT to confirm a suspected clot.
Symptoms
- A blood clot in a leg (DVT) — swelling, pain
- A clot travelling to the lungs (pulmonary embolism) — breathlessness, chest pain
- Stroke or mini-stroke, especially at a younger age
- Recurrent miscarriage or later pregnancy loss and complications
- A lacy purple skin mottling (livedo reticularis)
- Low platelet count
- Migraine APS is often silent until a clot or pregnancy loss brings it to light.
Related symptoms
Related lab panels
When to discuss with a doctor
APS should be considered — and its antibodies tested — after an unprovoked or unusually young blood clot, a clot in an unusual site, a stroke at a young age, or recurrent miscarriage. Because transient antibody positives follow infections, a single positive is not enough; the diagnosis needs a repeat 12 weeks later, interpreted by a specialist. A confirmed diagnosis is managed with blood-thinning treatment to prevent further clots, and in pregnancy with a specific regimen that substantially improves outcomes. An acute clot — a swollen painful leg, sudden breathlessness, stroke symptoms — is an emergency. Mediora.AI can flag a prolonged APTT, low platelets or a raised D-dimer as part of the picture; the diagnosis and anticoagulation belong with haematology or rheumatology.