Antiphospholipid syndrome (APS) is a disorder characterised by recurrent arterial or venous thrombosis and/or pregnancy losses, in the presence of persistently elevated levels of anticardiolipin antibodies and/or evidence of circulating lupus anticoagulant (these abnormalities are detected by blood tests). Primary APS occurs when there is no evidence of associated diseases. APS in the presence of an underlying disease, usually systemic lupus erythematosus, is called secondary APS.