Anticoagulation, recurrent thrombosis, and major bleeding in antiphospholipid syndrome: UK multicenter observational study.

abstractAntiphospholipid syndrome (APS) is an acquired autoimmune disease characterized by the presence of thrombosis and/or pregnancy morbidity with persistently positive antiphospholipid antibodies (aPL). Due to the heterogeneity and relative rarity of this disorder, clinical practice in the management of APS remains varied. In this retrospective UK-wide multicenter study, we aimed to delineate clinical practice and outcomes in thrombotic APS to improve the areas of limited knowledge, particularly anticoagulant practice, thrombotic recurrence, and bleeding. Anticoagulation in Antiphospholipid Syndrome is the largest multicenter observational study to date, spanning 20 National Health Service trusts in the UK, and including 500 adult patients (aged ≥18 years) with thrombotic APS, on or off anticoagulation during 2012-2021. Thrombotic APS is primarily treated with vitamin K antagonists; however, the rates of recurrent thrombosis remain high. In the last decade, recurrent thrombosis occurred in 43 of 125 (34.4%), 31 of 95 (32.6%), and 37 of 93 (39.8%) patients with single-, dual-, and triple-positive aPL, respectively, with a recurrence rate of 46%. There was no difference in the probability of recurrent thrombosis based on the number of positive aPL tests (P = .82), especially in the first 3 years. However, the probability of recurrent thrombosis was significantly higher in patients with lupus anticoagulant (P< .01) compared with the presence of other antibodies. There was a higher probability of recurrence in patients with arterial than venous thrombosis (P = .03). Overall, the 10-year bleeding rate was 22.0%, with 6.7% of patients having major bleeding. Identifying patients with APS at higher risk of recurrent thrombosis remains a challenge, and current risk stratification is not adequate.