Antiphospholipid Syndrome

Antiphospholipid syndrome (APS) is the most common acquired thrombophilia and is characterized by the occurrence of arterial, venous, and/or microvascular thromboses and pregnancy morbidity, frequently accompanied by hematologic alteration, such as thrombocytopenia and hemolytic anemia, in the presence of antiphospholipid antibodies (aPL). Some estimates indicate that the incidence of APS is around 1-2 new cases per 100,000 persons per year and the prevalence is around 6-50 cases per 100,000 persons. APS is diagnosed in 10-15% of patients with systemic lupus erythematosus, 9.5% of patients with deep vein thrombosis, 17% of patients with stroke younger than 50 years old, and 6% of patients with pregnancy morbidity. The original classification criteria for the APS were formulated at a workshop in Sapporo, Japan, in 1998, during the 8th International Congress on aPL and revised during another workshop in Sydney, Australia, in 2004, at the 11th International Congress on aPL. At least one clinical (vascular thrombosis or pregnancy morbidity) and one laboratory (presence of anticardiolipin IgG and/or IgM, anti-β2-glycoprotein I IgG and/or IgM, or lupus anticoagulant in at least 2 occasions at least 12 weeks apart) criterion had to be met for the classification of APS. Over the past decade, substantial evidence has accumulated on different clinical and laboratory aspects of APS, leading to the development of the new APS classification criteria, endorsed by the American College of Rheumatology (ACR) and the European Alliance of Associations for Rheumatology (EULAR), in 2023.