Does the anti-prothrombin antibodies measurement provide additional information in patients with thrombosis?

The aim of this study is to get new insight into the relevance of IgG anti-prothrombin antibodies in patients with thrombosis and to determine whether human prothrombin alone (aPT) or complexed to phosphatidylserine (aPS/PT) should be preferentially used for measuring these antibodies by enzyme-linked immunosorbent assay (ELISA). To this end, prevalence of anti-prothrombin antibodies, their characteristics in terms of avidity and heterogeneity, and their relationship with anti-β2 glycoprotein I antibodies (aβ2GPI) were studied in 152 patients with thrombosis. Patients were divided into two groups according to the presence or absence of antiphospholipid antibodies (aPL), called aPL+ or aPL−, respectively. In the aPL− group (n=90), the prevalence of anti-prothrombin antibodies was substantial (10%) but not significantly different from that of control (5%). In the aPL+ group (n=62), lupus anticoagulant (LA) or anticardiolipin antibodies (aCL) positive, 61% were positive for anti-prothrombin antibodies with no statistical difference between aPT and aPS/PT prevalence (42% vs. 55%, respectively). In the whole thrombotic population, 19% were only aPT and 34% only aPS/PT suggesting the presence of different antibodies. Absorption experiments confirmed the heterogeneity of aPT and aPS/PT. No difference in their avidity was demonstrated. From the aPL+ group, 60 were LA positive. Among them, 18% were negative for aβ2GPI and anti-prothrombin antibodies showing that the detection of these antibodies could not substitute for LA determination. In conclusion, our data show that the screening of the different anti-prothrombin antibodies is not warranted in the aPL+ group since these antibodies do not provide additional information compared to aCL, LA and/or aβ2GPI measurement. Nevertheless, the substantial prevalence of anti-prothrombin antibodies in the aPL− group should be further explored in a large prospective study.