Classification criteria for the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is based upon presence of clinical and laboratory criteria. The clinical criteria comprise pregnancy morbidity (according to strict definitions) en vascular thrombosis. Presence of so-called antiphospholipid antibodies (aPL) is the laboratory criterion. Under the umbrella of aPL fall both lupus anticoagulants, IgG and IgM anticardiolipine antibodies, and IgG and IgM anti-β2 glycoprotein antibodies. The diagnosis of APS heavily relies on these laboratory criteria, in particular because the clinical features are not rare in the general population. This chapter deals with the development and current use of classification criteria for APS. The problems with definitions of a positive laboratory tests, which resulted in a lot of confusion in the field and the practical use of aPL profiles, are highlighted. It is concluded that laboratory criteria for obstetric and thrombotic APS probably should be different; that aPL should be considered as risk factors in the context of other risk factors for thrombosis, cardiovascular disease, and pregnancy complications; and that there is a need for well-designed clinical studies to answer the many questions in the field.