Antiphospholipid syndrome !
An autoimmune disorder in which antibodies make the blood clot too easily, causing thrombosis and pregnancy losses.
Updated 2026-11-01
Structures involved
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- Femoral vein
- Kidneys
- Popliteal vein
- Great saphenous vein
- Vessels inside the kidney
- Middle cerebral artery
In the clinical exam
Why it happens
- Thrombosis and Virchow's triad
- Arterial vs venous thrombi; mural thrombi and lines of Zahn
- Hypercoagulable states: inherited and acquired
- The coagulation cascade
- Coagulation tests: PT/INR, aPTT and platelets
- Placenta
What it is
An acquired autoimmune thrombophilia in which persistent antiphospholipid antibodies cause venous, arterial or small-vessel thrombosis and/or pregnancy complications such as recurrent loss, stillbirth and early preeclampsia.
Who gets it
Most often diagnosed in young and middle-aged adults, more commonly in women. It may be primary or associated with systemic lupus erythematosus, in which many patients carry these antibodies. It is a recognised cause of thrombosis in young people and of recurrent pregnancy loss in Colombia and the rest of Latin America.
Causes
- Autoimmune; antibodies against phospholipid-binding proteins (beta-2 glycoprotein I, prothrombin)
- Primary, or secondary to lupus and other autoimmune diseases
- Transient antibodies can appear with infections and drugs and do not by themselves define the syndrome
Risk factors
- Systemic lupus erythematosus
- Triple positivity (lupus anticoagulant, anticardiolipin and anti-beta-2 glycoprotein I)
- Additional thrombotic triggers: pregnancy, oestrogen-containing contraceptives, surgery, immobility, smoking
- Previous thrombosis
Pathophysiology
The antibodies bind beta-2 glycoprotein I on cell surfaces, activating endothelium, platelets and monocytes, increasing tissue factor and activating complement, which tips the balance toward clotting. In the placenta they impair trophoblast invasion and cause inflammation and thrombosis of placental vessels, leading to loss, growth restriction or preeclampsia. Paradoxically, lupus anticoagulant prolongs clotting tests in the laboratory although it causes thrombosis in the body.
Classification
- Primary antiphospholipid syndrome
- Antiphospholipid syndrome associated with lupus or another autoimmune disease
- Thrombotic versus obstetric antiphospholipid syndrome
- Catastrophic antiphospholipid syndrome: multiple organ thromboses within days
Symptoms and signs
- Deep vein thrombosis of the legs, often unprovoked or in unusual sites
- Pulmonary embolism
- Stroke or transient ischaemic attack in a young adult
- Recurrent early miscarriages, fetal death, or early severe preeclampsia or placental insufficiency
- Livedo reticularis (net-like purple skin pattern)
- Low platelet count
- Heart valve thickening (Libman-Sacks endocarditis)
Diagnosis
- Clinical
- Combination of a clinical event (thrombosis or typical pregnancy morbidity) with persistently positive antibodies; the 2023 ACR/EULAR classification criteria weigh clinical and laboratory domains.
- Tests
- Lupus anticoagulant (clotting assays), anticardiolipin and anti-beta-2 glycoprotein I antibodies, positive on two occasions at least 12 weeks apart. Complete blood count (thrombocytopenia), aPTT, kidney function and urinalysis, ANA and other lupus tests.
- Imaging
- Compression ultrasound for DVT, CT pulmonary angiography for embolism, brain MRI for stroke, Doppler and obstetric ultrasound to follow placental flow and fetal growth, and echocardiography for valve disease.
Differential diagnosis
- Inherited thrombophilias (factor V Leiden, prothrombin mutation, protein C/S or antithrombin deficiency)
- Cancer-associated thrombosis
- Heparin-induced thrombocytopenia
- Thrombotic thrombocytopenic purpura and haemolytic uraemic syndrome
- Disseminated intravascular coagulation
- Other causes of recurrent pregnancy loss (chromosomal, uterine, endocrine)
Goal of treatment
Prevent first or recurrent thrombosis and pregnancy complications by anticoagulation suited to the clinical profile, while balancing bleeding risk.
Treatment
- Acute
- Acute thrombosis is treated with heparin (unfractionated or low-molecular-weight), followed by long-term oral anticoagulation; catastrophic APS needs ICU care with anticoagulation, glucocorticoids and plasma exchange or intravenous immunoglobulin.
- Medical
- After thrombosis, long-term vitamin K antagonist (warfarin) is the standard; direct oral anticoagulants are avoided, especially in triple-positive or arterial disease, because of more recurrent events.
- Medical
- In pregnancy, warfarin is replaced by low-molecular-weight heparin, usually with low-dose aspirin; hydroxychloroquine is often added in lupus-associated disease.
- Follow-up
- INR monitoring on vitamin K antagonists, platelet count on heparin, and close obstetric follow-up with fetal growth and Doppler surveillance; nursing care teaches bleeding precautions and medication adherence.
- Lifestyle
- Control of other vascular risk factors: no smoking, avoidance of oestrogen-containing contraceptives, mobilisation and thromboprophylaxis around surgery or immobility.
Complications
- Recurrent venous and arterial thrombosis
- Post-thrombotic syndrome and chronic thromboembolic pulmonary hypertension
- Stroke and cognitive impairment
- Pregnancy loss, preeclampsia, placental insufficiency and preterm birth
- Antiphospholipid nephropathy and kidney failure
- Catastrophic antiphospholipid syndrome with high mortality
- Bleeding from anticoagulation
Prognosis
With adequate anticoagulation the risk of recurrence falls, but it is lifelong after thrombosis. Most treated pregnancies end in a live birth. Arterial events, triple positivity and catastrophic APS carry a worse prognosis.
Prevention
- Avoiding oestrogen-containing contraceptives in antibody-positive women
- Thromboprophylaxis during high-risk situations (surgery, immobility, pregnancy and the puerperium)
- Not smoking and controlling blood pressure and lipids
Test yourself
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Which three laboratory tests define antiphospholipid antibodies?
Lupus anticoagulant, anticardiolipin and anti-beta-2 glycoprotein I antibodies, positive on two occasions at least 12 weeks apart.
Why is the term 'lupus anticoagulant' paradoxical?
It prolongs clotting tests such as the aPTT in vitro but causes thrombosis in vivo.
What is the long-term anticoagulant of choice after thrombosis in antiphospholipid syndrome?
A vitamin K antagonist (warfarin); direct oral anticoagulants are avoided, particularly in triple-positive patients.
How is anticoagulation managed in pregnancy in antiphospholipid syndrome?
Warfarin is teratogenic, so low-molecular-weight heparin is used, usually with low-dose aspirin.
Which obstetric outcomes suggest antiphospholipid syndrome?
Recurrent early miscarriages, unexplained fetal death after 10 weeks, and early severe preeclampsia or placental insufficiency.
Related conditions
- Deep vein thrombosis
- Pulmonary embolism
- Ischaemic stroke
- Miscarriage (early pregnancy loss)
- Preeclampsia
- Placental abruption
- Systemic lupus erythematosus
- Myocardial Infarction (Heart Attack)
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Antiphospholipid syndrome (MedlinePlus Genetics (U.S. National Library of Medicine), 2022).
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