Antiphospholipid syndrome (APS) is a clinical and laboratory entity consisting of persistent antibodies directed against phospholipid (aPL) in conjunction with recurrent venous or arterial thrombosis and obstetric signs.
Circulating lupus anticoagulant, measured by International Society on Thrombosis and Haemostasis (ISTH) criteria
Anticardiolipin antibodies (IgG or IgM), in moderate or high titre (> 40 GPL or MPL, or > 99th percentile), measured by a standardised ELISA
Anti-ß2-glycoprotein-I antibodies (IgG or IgM), present in titre > 99th percentile, measured by a standardised ELISA
APS can occur even in the absence of any autoimmune disease, in which case it is referred to as primary APS.
Where it arises in a patient presenting an autoimmune disease, the term "secondary APS" is used.
If an autoimmune disease is diagnosed in a patient with primary APS, the latter is subsequently referred to as secondary APS.