Antiphospholipid syndrome (APS) is an autoimmune disease that increases the risk of thrombosis as a result of procoagulatory antibodies. The condition may be idiopathic or acquired secondary to an underlying disease, such as systemic lupus erythematosus. Circulating antibodies deactivate anticoagulatory proteins and activate platelets, thereby inducing a hypercoagulable state. Typical clinical manifestations include recurring venous and arterial thrombotic events such as deep vein thromboses, strokes, or transient ischemic attacks. A severe complication of APS in women is recurrent miscarriages of healthy fetuses. The condition should be suspected in patients with a history of thrombosis or miscarriages. It is confirmed by detecting serum antiphospholipid antibodies (e.g., lupus anticoagulant, cardiolipin antibodies). Acute thrombotic events are treated with low-molecular-weight heparin and high-dose glucocorticoids to eliminate antibodies. In mild cases, long-term management involves prophylaxis with low dose aspirin; for patients at high risk of thrombotic events, warfarin is the drug of choice.
- Formation of procoagulatory antiphospholipid antibodies
- Induction of a hypercoagulable state → ↑ risk of thrombosis and embolism 
APS usually manifests with recurring thrombotic events that may affect any organ.
- Capillaries: splinter hemorrhages
- Pregnancy-related: recurrent miscarriages and premature births
- History 
Serology: for antiphospholipid antibodies
Lupus anticoagulant (LA): leads to a prolonged aPTT
- Mixing study: The patient's plasma is mixed with normal plasma. If the prolonged aPTT is caused by a lack of clotting factors, the factors contained in the normal plasma will normalize the aPTT. In the presence of lupus anticoagulants, the aPTT will remain unchanged.
- Dilute Russell viper venom test: Lupus anticoagulant interacts with Russell viper venom, which usually induces the formation of blood clots. As LA binds the venom, this effect is suppressed, resulting in a prolonged aPTT.
- Anticardiolipin antibodies (IgG and IgM): patients with APS often test false positive for syphilis (positive VDRL or RPR), as the antigen used in syphilis tests is cardiolipin.
- Anti-β2-glycoprotein antibodies: a group of antibodies that inactivate anticoagulant proteins (e.g., protein C, protein S, antithrombin III) and activate platelets and vascular endothelium, thereby resulting in a hypercoagulable state
- Lupus anticoagulant (LA): leads to a prolonged aPTT
- Blood tests
The key element of APS treatment is systemic anticoagulation.
- Acute management
- Secondary prophylaxis