What is Antiphospholipid Syndrome?
Antiphospholipid syndrome is an autoimmune condition in which antibodies make the blood more likely to clot. It causes deep vein thrombosis, stroke at a young age, and recurrent miscarriage. It is diagnosed by persistently positive antibodies alongside a clot or a defined pregnancy complication, and it is highly manageable once identified.
Also called: APS, Hughes syndrome, sticky blood syndrome
Who gets Antiphospholipid Syndrome?
It can occur on its own or alongside lupus, where up to a third of patients have the antibodies. It is a leading treatable cause of stroke in adults under 50 and of recurrent pregnancy loss. Antiphospholipid antibodies also appear transiently after infections without causing disease, which is why the diagnosis requires them to be positive twice, at least twelve weeks apart.
What are the symptoms of Antiphospholipid Syndrome?
Not everyone has every symptom below, and having one does not confirm the diagnosis. These are the features that most often lead to assessment:
- Deep vein thrombosis — a painful, swollen calf
- Pulmonary embolism — sudden breathlessness and chest pain
- Stroke or transient ischaemic attack at an unusually young age
- Recurrent early miscarriage, or later pregnancy loss
- Severe pre-eclampsia or growth restriction in pregnancy
- A lace-like purple mottling of the skin (livedo reticularis)
- Low platelet count
- Migraine, memory difficulty or seizures in some patients
- Heart valve abnormalities
How is Antiphospholipid Syndrome diagnosed?
Three antibodies are tested: lupus anticoagulant, anticardiolipin and anti-beta-2 glycoprotein I. Positive results must be confirmed at least twelve weeks later, because transient positivity after infection is common and does not indicate the syndrome.
Diagnosis requires persistent antibodies together with a clinical event — a confirmed clot or a defined pregnancy complication. Antibodies alone, without an event, are not antiphospholipid syndrome, though they do raise risk and change how other risk factors are managed.
Screening for lupus is part of the assessment.
How is Antiphospholipid Syndrome treated?
After a clot, long-term anticoagulation is the treatment, usually with warfarin monitored by INR. Direct oral anticoagulants are not recommended for high-risk (triple-positive) patients, in whom warfarin performs better.
In pregnancy, low-dose aspirin combined with low molecular weight heparin substantially improves live birth rates, and pregnancies are managed jointly with obstetrics.
For antibody-positive patients who have never had a clot, low-dose aspirin may be considered, and modifiable risks — smoking, combined oral contraceptives, immobility, uncontrolled blood pressure — are addressed carefully. Hydroxychloroquine is often added where lupus coexists.
Living with Antiphospholipid Syndrome
Anticoagulation is usually lifelong after a clot, with the practical implications that carries: INR monitoring, care with other medicines, and telling any surgeon or dentist before a procedure. Combined oral contraceptives are avoided. Long flights, surgery and immobility need planned prophylaxis. With treatment, most patients avoid further clots and most who want children have successful pregnancies.
When should you see a rheumatologist?
A clot with no obvious cause, a stroke under 50, or three or more early miscarriages should prompt testing for antiphospholipid antibodies. So should a clot in someone already diagnosed with lupus.
Common questions about Antiphospholipid Syndrome
I have the antibodies but never had a clot. Do I have APS?
No. The syndrome requires persistently positive antibodies together with a clinical event — a clot or a defined pregnancy complication. Antibodies alone raise risk and change how other risk factors are managed, but they are not the disease.
Can I have a healthy pregnancy with APS?
Yes. With low-dose aspirin and heparin, live birth rates improve substantially, and most women with APS who want children have successful pregnancies. Care is shared with an obstetric team from early in the pregnancy.
Why warfarin rather than the newer tablets?
For high-risk patients with all three antibodies positive, trials showed more clots on direct oral anticoagulants than on warfarin. Warfarin with INR monitoring remains the safer choice in that group.
Is anticoagulation lifelong?
After an unprovoked clot in confirmed APS, usually yes. The risk of recurrence on stopping is high, and this is reviewed periodically rather than assumed permanent without discussion.
This page is general information to support a consultation. It is not a diagnosis, and it does not replace an assessment by a doctor who has examined you.