Pos0728 Observations on the 2023 Acr/Eular Antiphospholipid Syndrome Classification Criteria: Data From a Monocentric Cohort of 205 Patients With Primary Aps

Background: The new 2023 ACR/EULAR antiphospholipid syndrome (APS) classification criteria 1 have a higher specificity compared to the Sapporo criteria 2. The novelties in the new criteria are: 1) the scoring system, since at least 3 points from clinical domains AND at least 3 points from laboratory domains are required; 2) the distinction between anticardiolipin (aCL) or anti-β2-glycoprotein I (aβ2GPI) IgG vs. IgM isotypes, having isolate IgM positivity a low weight, insufficient for APS classification; 3) aCL and aβ2GPI thresholds are defined as moderate (40-79 units) and high positivity (>80 units), despite the use of fixed cut-off values is not supported by the literature 3. Objectives: We aimed to verify the performance of the 2023 ACR/EULAR APS classification criteria in a cohort of primary (without systemic autoimmune diseases) vascular APS patients (PAPS), previously classified according to the Sapporo criteria. Methods: A cohort of PAPS patients with previous arterial, venous, or small-vessel manifestations attending our clinic was collected from 1992 to 2023. Clinical parameters were recorded at the start of follow-up, when two consecutive positive aPL antibody results were obtained more than 12 weeks apart, and updated as needed. Patients should meet the Sapporo classification criteria, and were re-evaluated to identify cases that would not be classified as PAPS based on the 2023 ACR/EULAR APS classification criteria. Results: Our cohort included 205 PAPS patients. Of them, 171 patients were classified as PAPS also according to the new ACR/EULAR criteria, while 34 (16.6%) did not: 23 due to insufficient score in the laboratory domain, caused by isolate IgM positivity; 11 due to the presence of aPL at a titer > 99° percentile but Conclusion: In this report, we showed that 16.6% of PAPS patients classified according to the Sapporo criteria would not meet the new ACR/EULAR classification criteria for APS. In clinical practice, this could result in the lack of adequate antithrombotic therapy, exposing these patients to the risk of a new thrombotic event. REFERENCES: 1 Barbhaiya M, et al. Ann Rheum Dis. 2023;82:1258-70. 2 Miyakis S, et al. J Thromb Haemost 2006;4:295-306. 3 Vandevelde A, et al. J Thromb Haemost. 2022;20:508-24. Acknowledgements: NIL. Disclosure of Interests: Margherita Zen GSK Astrazeneca, Marta Tonello: None declared, Antonia Calligaro: None declared, Maria Favaro: None declared, Teresa Del Ross: None declared, Filippo Vesentini: None declared, Federico Arru: None declared, Ilenia Anna Gennaio: None declared, Greta Hulej: None declared, Amelia Ruffatti: None declared, Andrea Doria: None declared.