2023 ACR/EULAR classification criteria for antiphospholipid syndrome: more lights rise but shade remains

Abstract

Antiphospholipid syndrome (APS) is an autoimmune disorder for which there are no universally accepted diagnostic criteria, although classification criteria do exist, as is the case with most autoimmune diseases. Until 2023, the 2006 Sydney classification criteria were in use. Although originally intended for research purposes, these criteria have often been employed in clinical practice as a substitute for diagnostic guidelines, thereby conflating classification with diagnosis. In July 2023, ACR and European Alliance of Associations for Rheumatology convened a panel of experts to revise these criteria. The newly published classification criteria are explicitly intended for research use only. They place a strong emphasis on specificity—99%—but this comes at the expense of sensitivity—84%. The updated criteria encompass six clinical domains and two laboratory domains. Notably, the inclusion of new clinical features, such as thrombocytopenia, cardiac valve involvement and microvascular thrombosis, has broadened patient inclusion and, indirectly, aided the diagnostic process. However, a significant proportion of patients with suspected antiphospholipid antibody-related conditions may no longer meet the criteria for APS classification. In real-world settings, this could result in these individuals being denied appropriate management, thereby increasing their risk of subsequent thrombotic or obstetric events, as has already been demonstrated. This manuscript examines the advantages and limitations of the new clinical and laboratory domains, considering their implications not only from a research but also from a clinical perspective, APS.