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 < 40 units. Notably, 9 out of 34 (26%) patients not classified according to the new ACR/EULAR criteria had a provoked relapse (thrombotic event) during the follow-up, confirming a pro-thrombotic profile. Demographic and clinical characteristics and follow-up of these 9 patients are summarized in Table 1. The comparison between the confirmed and unconfirmed PAPS patients is showed in Table 2. No clinically relevant differences were identified between the two groups. During follow-up, 11 patients died, all belonging to the group of confirmed PAPS patients. 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.