Antiphospholipid syndrome (APS), also called Hughes syndrome, is an autoimmune disorder in which antibodies directed against phospholipid-binding proteins drive recurrent arterial or venous thrombosis, microvascular disease, and pregnancy morbidity. It affects approximately 40-50 per 100,000 adults, accounts for roughly 10-15% of all deep vein thromboses and around 20% of strokes in adults under 50, and is the most common acquired cause of recurrent pregnancy loss.
Antiphospholipid syndrome (ICD-10: D68.61) is a systemic autoimmune disorder characterized by venous, arterial, or microvascular thrombosis, pregnancy morbidity, or both, in patients with persistent antiphospholipid antibodies. The pathogenic antibodies — lupus anticoagulant (LA), anti-cardiolipin (aCL), and anti-β2-glycoprotein-I (anti-β2GPI) — bind plasma proteins that interact with phospholipids on endothelial cells, platelets, monocytes, and trophoblasts, activating coagulation, complement, and inflammation. The 2023 ACR/EULAR classification criteria (replacing the Sapporo 2006 criteria) require persistent positivity on at least two tests 12 weeks apart together with clinical manifestations weighted by domain (macrovascular venous and arterial thrombosis, microvascular disease, obstetric morbidity, cardiac valve disease, and thrombocytopenia). APS is described as primary when no other autoimmune disease is present, or secondary when it occurs alongside systemic lupus erythematosus, Sjögren syndrome, rheumatoid arthritis, or other connective tissue disease.
The key symptoms of Antiphospholipid Syndrome are: Deep vein thrombosis of the legs, often unprovoked or recurrent despite standard prophylaxis, presenting with calf swelling, pain, and warmth., Pulmonary embolism with sudden chest pain, breathlessness, haemoptysis, or syncope., Ischaemic stroke or transient ischaemic attack in adults under 50 with unilateral weakness, slurred speech, or visual loss., Recurrent first-trimester miscarriages (three or more) or fetal loss after 10 weeks of pregnancy., Pre-eclampsia, severe placental insufficiency, intrauterine growth restriction, or premature delivery before 34 weeks., Livedo reticularis: persistent mottled purplish skin pattern on the legs, arms, or trunk that does not fade with warming., Mild to moderate thrombocytopenia (platelet count typically 50-140 × 10⁹/L) without significant bleeding..
Diagnosis combines clinical features with persistent laboratory evidence of antiphospholipid antibodies. The 2023 ACR/EULAR APS classification criteria require an entry criterion (at least one clinical event and at least one positive antiphospholipid antibody test) plus a weighted score across six domains: macrovascular venous thromboembolism, macrovascular arterial thrombosis, microvascular disease, obstetric morbidity, cardiac valve disease, and haematological. Laboratory testing uses three assays: lupus anticoagulant (LA, performed by dilute Russell viper venom time and activated partial thromboplastin time mixing studies), anti-cardiolipin IgG and IgM (ELISA, with high titre defined as ≥40 GPL or MPL units), and anti-β2-glycoprotein-I IgG and IgM (ELISA, high titre ≥40 units). Any positive test must be repeated after at least 12 weeks to confirm persistence — single positive results are not diagnostic. Patients are stratified as low-, medium-, or high-risk based on antibody profile (single vs triple positivity) and titre. Additional investigations include full blood count for thrombocytopenia, prothrombin time, activated partial thromboplastin time, fibrinogen, D-dimer, renal function, liver function, antinuclear antibody and complement (to screen for lupus), echocardiogram for valve disease, and imaging for current or past thrombosis (Doppler ultrasound for DVT, CTPA for pulmonary embolism, MRI brain for stroke or ischaemic lesions). Genetic thrombophilia testing (factor V Leiden, prothrombin gene, antithrombin, protein C and S) is performed in selected cases. Differential diagnosis includes inherited thrombophilia, heparin-induced thrombocytopenia, paroxysmal nocturnal haemoglobinuria, myeloproliferative disorders, thrombotic thrombocytopenic purpura, atypical haemolytic uraemic syndrome, vasculitis, and infective endocarditis.
Outcome depends on antibody profile, end-organ damage, and adherence to anticoagulation. Patients with single-antibody, single-event APS on appropriate warfarin therapy have annual recurrence rates of 1-3% and near-normal life expectancy. Triple-positive patients face higher recurrence (5-7% per year even on warfarin) and worse vascular outcomes; cumulative 10-year survival is 85-90% in modern cohorts. Catastrophic APS still carries 30-50% mortality despite treatment. Quality of life is reduced by chronic anticoagulation, fear of recurrence, cognitive complaints, and pregnancy complications, but most patients lead full lives. Obstetric APS outcomes have transformed: live-birth rates rose from below 30% (no treatment) to 70-80% with aspirin and heparin combination therapy. Long-term morbidity includes post-thrombotic syndrome, chronic thromboembolic pulmonary hypertension, vascular dementia, and accelerated atherosclerosis; aggressive cardiovascular risk reduction is essential.
A rheumatologist or haematologist with expertise in APS confirms persistent antibody positivity, classifies risk, plans the right anticoagulant strategy, and coordinates obstetric and stroke care. Multidisciplinary follow-up is essential, particularly during pregnancy and around surgery, because incorrect anticoagulation strategy is a leading cause of recurrent thrombosis and obstetric loss.
Find specialists →After acute venous thrombosis, symptoms improve over 2-4 weeks with anticoagulation; post-thrombotic syndrome may persist. Stroke recovery follows standard neurorehabilitation. Pregnancy outcomes are best when treatment starts before conception. Lifelong anticoagulation is the norm; some patients with low-risk profiles may stop anticoagulation under specialist supervision after sustained antibody seronegativity over years.
Encourage 150 minutes weekly of moderate aerobic activity (walking, swimming, cycling) plus resistance training twice weekly. Avoid contact sports and activities with high bleeding risk. After acute thrombosis, gradual return to activity at 4-6 weeks under medical advice.
Choose a centre with a dedicated APS or thrombosis clinic, access to high-quality lupus anticoagulant and anti-β2GPI testing, anticoagulation monitoring service, high-risk obstetric clinic, and an established stroke pathway. Ask about experience with catastrophic APS, pregnancy outcomes, and use of DOACs in selected cases.
Medically reviewed by AIHealz Medical Editorial Board · May 13, 2026
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