Synopsis
Diagnose antiphospholipid syndrome from a compatible thrombotic or obstetric event plus persistent laboratory evidence, choose event-specific antithrombotic treatment, and recognise catastrophic disease, testing interference and pregnancy risk.
- APS requires a relevant clinical event and persistent antiphospholipid antibodies; an isolated positive test without thrombosis or defined pregnancy morbidity is not the syndrome.
- Order lupus anticoagulant, IgG and IgM anticardiolipin and IgG and IgM anti-beta-2-glycoprotein-I, then confirm clinically relevant positivity at least twelve weeks later.
- Anticoagulants interfere with lupus-anticoagulant assays, so record the exact agent, timing and laboratory strategy; never stop necessary anticoagulation unsafely just to obtain a cleaner test.
- Treat an acute VTE through the standard emergency pathway, then use a vitamin-K antagonist with target INR 2.0–3.0 for most first venous APS thromboses; duration is commonly long term after an unprovoked event.
- Avoid rivaroxaban in triple-positive APS and generally avoid DOAC substitution in high-risk APS because recurrent events, particularly arterial events, are increased.
- For arterial APS, recurrent thrombosis or bleeding constraints, haematology individualises warfarin intensity, possible low-dose aspirin and investigation of adherence, INR control and competing mechanisms.
- Obstetric APS without previous thrombosis is usually managed with low-dose aspirin plus prophylactic LMWH from a positive pregnancy test, continuing postpartum prophylaxis according to risk; previous thrombotic APS requires therapeutic anticoagulation.
- Catastrophic APS is a critical-care diagnosis: therapeutic heparin, high-dose glucocorticoid and plasma exchange or IVIG are combined while infection or another trigger is treated.
- Manage smoking, pressure, lipids, diabetes, obesity, immobility and oestrogen exposure; antibody status does not remove ordinary vascular prevention.
- Do not use the 2023 ACR/EULAR classification score as a diagnostic gate; classification serves research and clinical judgement remains essential.
Key red flags
New unilateral weakness, chest pain, hypoxia, painful swollen limb, mesenteric pain or limb ischaemia requires the appropriate acute arterial or venous thrombosis pathway.
Thrombosis in several organs within one week with laboratory or histological small-vessel occlusion requires urgent catastrophic APS assessment.
Pregnancy with pain, bleeding, hypertension, fetal compromise or thrombosis requires same-day obstetric and haematology review rather than routine anticoagulation adjustment.
Thrombocytopenia with schistocytes, haemolysis, fever, neurological or renal injury may represent TTP or another TMA and needs emergency plasma-exchange pathway assessment.
Major bleeding, head injury, melaena or haemodynamic change during anticoagulation requires immediate severity assessment and agent-specific reversal planning.
Three or more organ systems developing thrombosis over about one week with small-vessel occlusion suggests catastrophic APS and demands immediate combination care.
Neurological change, haemodynamic compromise, melaena, haematemesis or expanding bleeding on anticoagulation requires urgent reversal and source-control assessment.
Investigation priorities
Confirm the clinical event and define its vascular territory, severity and alternative mechanism.
Management branches
Thrombosis or a qualifying pregnancy history raises suspicion of APS.
- Confirm the event objectively, record provoking factors and obtain a complete obstetric, autoimmune, medicine, bleeding and family history.
- Send lupus anticoagulant, anticardiolipin and anti-beta-2-glycoprotein-I with exact anticoagulant details and coagulation-laboratory advice.
- Repeat relevant positivity after at least twelve weeks, then integrate antibody risk and clinical phenotype rather than diagnosing from one result.