Antibodies and Diagnostic Tests in Antiphospholipid Syndrome

The current classification criteria for antiphospholipid syndrome (APS) recommend testing for three assays, namely antibodies against cardiolipin (aCL) and β2-glycoprotein I (anti-β2GPI) plus lupus anticoagulant (LA). β2GPIdependent antibodies are those mainly responsible for the positivity in the APS laboratory assays and for most of the pathogenic mechanisms involved in the syndrome. To overcome the technical limitations of APS assays and to identify a broader spectrum of patients, several tests have been assessed as additional laboratory tools: antibodies against domain I of β2GPI, aCL, anti-β2GPI IgA and antibodies against PT are among the most promising but still under evaluation. Other nonclassification/diagnostic autoantibodies have been described in APS, some directly contributing to the clinical manifestations (antibodies against proteins involved in hemostasis, anti-platelet and anti-endothelial cell antibodies) and some others reflecting the ongoing systemic autoimmunity characteristic of the syndrome (anti-nuclear, anti-mitochondrial, anti-red cell, anti-thyroid antibodies, and antibodies against plasma lipoproteins).