Interest of IgG and IgM antiprothrombin autoantibodies in the exploration of antiphospholipid syndrome: a 5-year retrospective study

Objectives. Non-conventional aPL have been described in patients presenting clinical manifestations of antiphospholipid syndrome but negative for conventional markers. Among them, detection of autoantibodies against prothrombin has been proposed to improve diagnosis and management of these patients. However autoantibodies against prothrombin are heterogeneous and their use in clinical practice still remains unclear. The aim of this study was to evaluate the interest of IgG and IgM autoantibodies directed against the prothrombin only (aPT). Methods. We retrospectively studied IgM and IgG aPT results, conventional antiphospholipid syndrome markers and clinical data of a large cohort of 441 patients referred for antiphospholipid syndrome exploration with aPT detection over a period of 5 years. Results. We observed a total prevalence of 17% of aPT-positive patients (75/441). A significant association was found between aPT and thrombosis (P = 0.035), with 70% of patients having unexplained thrombosis, aPT representing the sole aPL detected. aPT positivity was significantly more frequent in venous thrombosis than in arterial thrombosis (P = 0.004). Interestingly, we demonstrated for the first time that aPT IgG levels were higher in recurrent thrombosis than in isolated thrombosis (P = 0.013), leading us to propose a predictive level of recurrence for thrombosis. Conclusion. Our results show that aPT are associated with thrombosis and demonstrate the interest of assessing both IgG and IgM aPT, in particular in venous thrombosis when conventional markers are negative. Quantification of aPT could predict recurrence of thrombosis and influence subsequent treatment strategy. Prospective clinical studies are now required to confirm these results.