Antiphospholipid antibody testing for the antiphospholipid syndrome: a comprehensive practical review including a synopsis of challenges and recent guidelines

The antiphospholipid (antibody) syndrome (APS) is an autoimmune condition characterised by a wide range of clinical features, but primarily identified as thrombotic and/or obstetric related adverse events. APS is associated with the presence of antiphospholipid antibodies (aPL), including the so-called lupus anticoagulant (LA). These aPL are heterogeneous in nature, detected with varying sensitivity and specificity by a diverse range of laboratory tests. All these tests are unfortunately imperfect, suffer from poor assay reproducibility (inter-method and inter-laboratory) and a lack of standardisation and harmonisation. Clinicians and laboratory personnel may struggle to keep abreast of these factors, as well as the expanding range of available aPL tests, and consequent result interpretation. Therefore, APS remains a significant diagnostic challenge for many clinicians across a wide range of clinical specialities, due to these issues related to laboratory testing as well as the ever-expanding range of reported clinical manifestations. This review is primarily focussed on issues related to laboratory testing for APS in regards to the currently available assays, and summarises recent international consensus guidelines for aPL testing, both for the liquid phase functional LA assays and the solid phase assays (anticardiolipin and anti-beta-2-Glycoprotein-l).