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.
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.
Three or more organ systems developing thrombosis over about one week with small-vessel occlusion suggests catastrophic APS and demands immediate combination care.
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.
Key medicines
Warfarin for venous thrombotic APSStart through an anticoagulation service with heparin overlap when treating acute VTE, individualising the daily dose to achieve INR 2.0–3.0; continue long term when recurrence risk outweighs bleeding risk.
Low-dose aspirinUse 75–100 mg orally once daily when the APS or pregnancy pathway specifically indicates antiplatelet treatment; UK obstetric protocols may use up to 150 mg at night for pre-eclampsia prevention.