2023 ACR/EULAR classification criteria in existing research cohorts: an international study.

Objective: To assess the impact of the updated ACR/EULAR APS classification criteria on two large research cohorts.

Methods: Consecutive patients who tested persistently positive for at least one aPL in the last three years were enrolled. The first APS Sydney index event was considered and computed for the comparison between Sydney and 2023 APS criteria. When computing the 2023 APS criteria, additional manifestations were also considered.

Results: The cohort comprised 249 patients (185 with APS and 64 aPL carriers according to Sydney criteria). The 185 patients had as first index event venous thrombosis in 55 cases (29.8%), arterial thrombosis in 63 (34%) and pregnancy morbidity in 67 (36.2%). When applying the updated criteria, 90 subjects (48.7%) failed to reach the composite score of the new criteria. The percentage of thrombotic APS per Sydney criteria decreased from 47.3% to 34.9% because of high cardiovascular risk in 23 cases, IgM aPL profile in six cases and in two patients for both reasons. Patients with pregnancy morbidity decreased from 26.9% to 3.2% (39 cases of recurrent early pregnancy loss and 20 of fetal losses). Consequently, the percentage of aPL carriers increased from 26% to 61%. When looking at the disease evolution at follow-up, 32 additional patients out of 90 (35.6%) fulfilled the new APS criteria, after developing additional clinical manifestation following index event.

Conclusion: When applying the new APS criteria to our research cohorts, not-negligible differences exist in patients' classification. A multidisciplinary approach will be mandatory to assess the impact of the new criteria on research and, ultimately, patients' care.