Choice of anticoagulation in patients with low risk antiphospholipid syndrome.

Antiphospholipid syndrome (APS) is an acquired hypercoagulable state necessitating long-term anticoagulation for secondary thrombosis prevention. Anticoagulation guidelines are predominantly based on data in high risk, triple positive patients, and favor Vitamin K antagonists over other forms of anticoagulation. The efficacy of alternative anticoagulants for secondary thrombosis prevention in low risk, single and double positive APS remains uncertain. This study aimed to assess the incidence of recurrent thrombosis and major bleeding for patient with low risk APS on long-term anticoagulation. We performed a retrospective cohort study of patients who met revised criteria for thrombotic APS between January, 2001 and April, 2021 and received care through the Lifespan Health System. Primary outcomes included recurrent thrombosis and WHO Grades 3 and 4 major bleeding. A total of 190 patients were followed over a median duration of 3.1 years. At time of APS diagnosis, 89 patients were treated with warfarin and 59 patients with a direct oral anticoagulant (DOAC). There were similar rates of recurrent thrombosis in low risk patients on warfarin versus DOACs (adjusted IRR 6.91; 95% CI 0.90-53.40, p = 0.064). Major bleeding events only occurred in low risk patients on warfarin (n = 8, log-rank p = 0.13). In conclusion, despite the choice of anticoagulation, patients with low risk APS had similar rates of recurrent thrombosis suggesting DOACs may be a potential treatment option for this cohort. There was a non-significant increase in major bleeding rates in low risk patients on warfarin versus DOACs. Study limitations include a retrospective study design and small event numbers.