CO097 | IMPACT OF THE 2023 ACR/EULAR ANTIPHOSPHOLIPID SYNDROME CRITERIA IN 1200 WOMEN WITH PRIOR OBSTETRIC ANTIPHOSPHOLIPID SYNDROME

J. Alijotas-Reig^1|2|3, E. Esteve-Valverde⁴, L. Saez-Comet⁵, A. Anunciacion-Llunell³, R. Ferrer-Oliveras⁶, E. Lefkou⁷, A. Mekinian⁸, C. Belizna⁹, A. Hoxha¹⁰, A. Tincani¹¹, L. Marozio¹², G. Espinosa¹³, S. de Carolis¹⁴, S. Udry¹⁵, J.O. Latino¹⁵, E. Llurba¹⁶, C.B. Chighizola^17|18, M. Gerosa¹⁹, V. Pengo²⁰, K. Lundelin²¹, P. Rovere-Querini²², V. Canti²², K. Mayer-Pickel²³, T. Reshetnyak²⁴, S. Tabacco²⁵, L. Stojanovich²⁶, B.A. Gonçalves²⁷, S. Morales-Perez¹, F. Miro-Mur³ | ¹Department of Medicine, Universitat Autonoma de Barcelona, Spain; ²Systemic Autoimmune Disease Unit, Department of Internal Medicine, Vall d’Hebron University Hospital, Spain; ³Systemic Autoimmune Diseases Research Unit, Vall d’Hebron Institut de Recerca, Barcelona, Spain; ⁴Systemic Autoimmune Diseases Unit, Department of Internal Medicine, Hospital Sant Camil, Consorci Sanitari del Garraf, Barcelona, Spain; ⁵Department of Internal Medicine, Hospital Universitario Miguel Servet, Zaragoza, Spain; ⁶Obstetrics Department, High-Risk Unit, Hospital Universitario Quironsalud, Barcelona, Spain; ⁷Haematology Unit, Hippokration Hospital of Thessaloniki, Greece; ⁸AP-HP, Hopital Saint-Antoine, Service de Medecine Interne and Inflammation-Immunopathology-Biotherapy Department (DHU i2B), Sorbonne Universites, Paris, France; ⁹Vascular and Coagulation Department, University Hospital Angers, Angers, France; ¹⁰Internal Medicine Unit, Thrombotic and Bleeding Disorder Center, University of Padua, Padova, Italy; ¹¹Department of Clinical and Experimental Sciences, University of Brescia, Spedali Civili, Brescia, Italy; ¹²Department of Obstetrics and Gynaecology, Universita di Torino, Torino, Italy; ¹³Systemic Autoimmune Diseases Service, Hospital Clínic, Universitat de Barcelona, Barcelona, Spain; ¹⁴Department of Gynaecology, Gemelli Hospital, Catholic University, Roma, Italy; ¹⁵Autoimmune, Thrombophilic Diseases and Pregnancy Division, Dr. Carlos G. Durand Hospital, Buenos Aires, Argentina; ¹⁶Obstetrics and Gynaecology Department, High-Risk Unit, University Hospital de la Santa Creu i Sant Pau, Barcelona, Spain; ¹⁷Department of Clinical Science and Community Health, University of Milano, Milano, Italy; ¹⁸Unit of Pediatric Rheumatology, ASST G. Pini-CTO, Milano, Italy; ¹⁹Division of Rheumatology, Department of Clinical Sciences and Community Health, University of Milano, Milano, Italy; ²⁰Cardiology Unit, Department of Cardiac, Thoracic and Vascular Sciences, University of Padua, Padova, Italy; ²¹Department of Pediatrics, Faculty of Medicine, University of Turku, Turku, Finland; ²²Internal Medicine and Division of Immunology, Transplantation and Infectious Diseases, IRCCS Ospedale San Raffaele, Milano, Italy; ²³Department of Obstetrics, Medical University of Graz, Graz, Austria; ²⁴Department of Systemic Rheumatic Disease, V. A. Nasonova Research Institute of Rheumatology, Moscow, Russia; ²⁵Department of Gynecology, Obstetrics and Urology, Sapienza University of Roma, Roma, Italy; ²⁶University Medical Center, University of Belgrade, Belgrade, Serbia; ²⁷Department of Internal Medicine, Hospital Sant Joan Despí Moises-Broggi, Barcelona, Spain

Background and aims. The 2023 ACR/EULAR classification criteria for antiphospholipid syndrome (APS) were developed to improve specificity, but concerns have emerged regarding their sensitivity, particularly in obstetric APS (OAPS). This study aimed to assess the impact of the new criteria on a large, well-characterized cohort of women previously classified with OAPS according to the Sydney criteria and to explore potential clinical implications of reclassification.
Methods. We analyzed 1,200 women included in the EUROAPS registry who fulfilled the 2006 Sydney classification criteria for obstetric APS. These cases were re-evaluated using the 2023 ACR/EULAR criteria, focusing on obstetric clinical manifestations (domain 4) and laboratory features (domain 8). The cohort included patients from 30 tertiary centers across Europe and Argentina. Descriptive analyses were performed to determine the proportion of patients remaining classifiable under the new framework and to identify the main factors driving exclusion.
Results. Application of the 2023 ACR/EULAR criteria led to a substantial reduction in classifiable cases. Based on clinical criteria alone, 68% of women were excluded, primarily due to the lower weighting of recurrent pregnancy loss and fetal death. Additional exclusions occurred when applying laboratory constraints, including reduced consideration of isolated IgM positivity and the introduction of fixed antibody thresholds. Overall, only 256 out of 1,200 women (21.3%) remained classifiable as OAPS. The main drivers of reclassification were the stringent scoring system in the obstetric domain, the non-cumulative nature of clinical items, and restrictive laboratory definitions.
Conclusions. In this large multicenter cohort, the 2023 ACR/EULAR criteria markedly reduced the number of women classified with obstetric APS compared with the Sydney criteria. While increased specificity may benefit research homogeneity, the significant loss of sensitivity raises concerns about under-recognition of clinically relevant disease. These findings highlight the need for careful clinical judgement and further prospective studies to refine classification strategies and ensure that patients at risk are not overlooked.