SAT0202 International Multi-Centre Study to Evaluate the Clinical Significance of Phosphatidylserine-Dependent Antiprothrombin Antibodies for the Diagnosis of Antiphospholipid Syndrome
Authors: O. Amengual, R. Forastiero, M. Sugiura-Ogasawara, K. Oku, K. Otomo, J. Alves, C. Favas, P. Žigon, A. Ambrožič, M. Tomšič, G. Ruiz-Irastorza, I. Ruiz-Arruza, M.L. Bertolaccini, G.L. Norman, Z. Shums, J. Arai, T. Atsumi
Journal: Annals of the Rheumatic Diseases (2014)

<h3>Background</h3> Antiprothrombin antibodies bind to prothrombin coated ELISA plates but also recognize prothrombin exposed to immobilized phosphatidylserine, namely phosphatidylserine-dependent antiprothrombin antibodies (aPS/PT). During the 13th International Congress on Antiphospholipid Antibodies (APLA 2010) a Task Force of worldwide scientists agreed that the antiprothrombin antibody assay, in particular, aPS/PT, would potentially contribute to a better recognition of antiphospholipid syndrome (APS). As a result, a retrospective, cross-sectional multi-centre study was designed. <h3>Objectives</h3> To determine the value of aPS/PT for the diagnosis of APS. <h3>Methods</h3> The study involved eight centres from 7 countries (Argentina, Japan, Portugal, Slovenia, Spain, United Kingdom and United States). Demographics and clinical/laboratory data from all the subjects were retrospectively collected. A serum/plasma sample from the subjects was prepared at each participant institution. Specimens were blinded and determination of IgG/IgM aPS/PT was performed at INOVA Diagnostics, Inc. San Diego, USA (INOVA) using ELISA kits provided by two manufacturers: Medical and Biological Laboratories Co. Ltd, Nagano Japan (MBL) and INOVA. <h3>Results</h3> Two hundred forty-seven subjects were included (126 APS patients, 73 non-APS patients and 48 healthy controls). Eighty three percent of samples showed concordant results for IgG and 82% for IgM aPS/PT using ELISA kits from both manufacturers. Statistically significant correlations in the IgG and IgM aPS/PT values were obtained using ELISAs from both manufacturers (r=0.827, r=0.625, p&lt;0.001, respectively). Samples were defined aPS/PT positive or negative based on concordant results in the INOVA and MBL assays. Samples with discrepant aPS/PT results were excluded from the subsequent analysis. One hundred ninety-nine samples had concordant aPS/PT results: 103 from APS patients, 51 from non-APS patients and 45 from healthy controls. IgG and/or IgM aPS/PT were more prevalent in APS patients than in patients without APS (63/61% vs. 10/20%), OR: 6.46 [95% CI 2.9-14.3], p&lt;0.0001. Three (7%) healthy subjects had IgG or IgM aPS/PT. Among all subjects in this study, sensitivity, specificity, positive predictive value and negative predictive value of aPS/PT for the diagnosis of APS was 61%, 86%, 83% and 67%, respectively. <h3>Conclusions</h3> Determination of aPS/PT using different commercial assays is reliable. aPS/PT detection offers an additional, easily performed laboratory parameter that may assist in the diagnosis of APS. <h3>Acknowledgements</h3> The authors want to acknowledge the contributions of the late Prof. Silvia Pierangeli, University of Texas Medical Branch, Galveston, TX, USA <h3>Disclosure of Interest</h3> O. Amengual: None declared, R. Forastiero: None declared, M. Sugiura-Ogasawara: None declared, K. Oku: None declared, K. Otomo: None declared, J. Alves: None declared, C. Favas: None declared, P. Žigon: None declared, A. Ambrožič: None declared, M. Tomšič: None declared, G. Ruiz-Irastorza: None declared, I. Ruiz-Arruza: None declared, M. Bertolaccini: None declared, G. Norman Employee of: INOVA Diagnostics Inc, Z. Shums Employee of: INOVA Diagnostics Inc., J. Arai Employee of: Medical and Biological Laboratories Co Ltd, T. Atsumi: None declared <h3>DOI</h3> 10.1136/annrheumdis-2014-eular.2426