Impact of the 2023 ACR/EULAR Classification Criteria on START2 Antiphospholipid Registry

Introduction: The recently published ACR/EULAR classification criteria score (3 points or more) both clinical and laboratory criteria to define the presence of antiphospholipid syndrome (APS). The clinical criteria have been better defined while laboratory criteria remain the same [lupus anticoagulant (LA), anticardiolipin (aCL) and anti ß2-Glycoprotein I (aß2GPI) antibodies] but with different impact (points) on the classification of patients. APS is excluded if more than 3 years separate positive test for antiphospholipid antibodies (aPL) and clinical manifestation. Methods: The present study evaluates how many patients would be excluded by the new criteria among those enrolled as APS in the START 2 antiphospholipid registry. The analysis includes 380 patients (274 APS and 106 carriers). Results: Of 274 patients classified as APS, 118 (43%) did not match the new ACR/EULAR criteria for various reasons. First, the determination of aCL and aß2GPI antibodies was performed by automated instrumentations not allowed in the new criteria. Second, laboratory test score was less than 3 and this was due to an isolated IgM aCL or IgM aß2GPI in most cases and to isolated LA unconfirmed after 12 weeks in few cases. Third, 2 patients had a positive laboratory tests more than 3 years after the clinical event. Of the 106 carriers, 62% had aCL and aß2GPI determined by ELISA thus meeting the ACL/EULAR laboratory criteria but were negative for clinical criteria. Discussion: This study shows that many patients classified as APS in the START 2 registry do not match the classification using the new ACR/EULAR criteria.