New classification criteria for antiphospholipid syndrome

APS is a systemic autoimmune disease associated with persistent antiphospholipid antibodies (APL). It can cause thrombosis and pregnancy complications as well as non-thrombotic manifestations such as cardiac valve disease.

Classification is important to help identify people to participate in research and ensures that similar disease conditions are included and compared in trials. This is different from tools that help doctors make a diagnosis.

The APS classification criteria were last revised in 2006, but understanding of the disease has evolved since then. EULAR and ACR worked together to develop a new APS classification system based on modern disease understanding. The intention was that the new tool would allow individual criteria and different risk profiles to be weighted and demonstrate excellent operating characteristics with the highest possible specificity. Four key phases were followed in the development of the standard: generation; reduction of items; Definition, further reduction, and weighting, threshold detection; And finally, validation.

After changes and revisions, the updated classification specifies an entry criterion of at least one positive aPL test within 3 years of detection of an aPL-related clinical criterion. This is followed by a set of weighted criteria, each scoring 1-7 points. Criteria are clustered into six clinical domains and two laboratory domains. Clinical domains are macrovascular venous thromboembolism, macrovascular arterial thrombosis, microvascular, obstetrics, cardiac valves, and hematology. Laboratory domains include assays and antibody tests to increase the specificity of criteria. Patients scoring at least 3 points from each of the clinical and laboratory domains were classified as APS.

The new classification criteria were tested in probable APS cases, with results showing good sensitivity and specificity. In fact, the specificity for the new classification system was 99%, compared to the 86% achieved with the original 2006 criteria. This is important, because classification criteria are based on standardized and strict definitions to ensure consistency in clinical trials, and therefore require very high specificity, even at the cost of sensitivity.

EULAR hopes that these new classification criteria will support high-quality, risk-stratified
Epidemiologic studies and clinical trials in APS, and ultimately lead to improved patient care and management recommendations.