Background 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.
Objectives To determine the value of aPS/PT for the diagnosis of APS.
Methods 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.
Results 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<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<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.
Conclusions 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.
Acknowledgements The authors want to acknowledge the contributions of the late Prof. Silvia Pierangeli, University of Texas Medical Branch, Galveston, TX, USA
Disclosure of Interest 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