OBJECTIVES: We aimed to explore the prevalence and risk factors for bleeding in patients with thrombotic antiphospholipid syndrome (tAPS) on antithrombotic therapy.

METHODS: Single-centre retrospective analysis of patients with tAPS (Sydney criteria). Bleeding events were classified according to the International Society on Thrombosis and Haemostasis as (a) major bleeding and (b) any bleeding. Risk factors for any bleeding and for major bleeding were explored using logistic regression.

RESULTS: We identified 197 patients (female, 71.1%; primary APS, 65.9%; presenting with arterial thrombosis, 44.2%; median disease duration, 10 years), all of whom had been exposed to antithrombotic therapy: anticoagulation, 98.5% (90.2% warfarin), and combined antithrombotic therapy, 24.9%. Eighty patients (40.6%) experienced 167 bleedings (22.8% major bleedings). Recurrent thrombosis during treatment occurred in 26.9% of patients (58.5% arterial thrombosis), and 41.9% of patients received high-intensity anticoagulation schemes (all warfarin target INR >3). Thrombocytopenia (<150 × 10⁹ platelets/L) affected 12.7% of patients. Secondary APS was associated with major bleeding, whereas recurrent thrombosis and high-intensity anticoagulation were associated with any bleeding. Combined antithrombotic therapy and thrombocytopenia increased the risk for any bleeding and major bleeding, with thrombocytopenia associated with both outcomes (OR = 5.58, 95% CI, 1.93-16.13; OR = 2.82, 95% CI, 1.06-7.51, respectively) after multivariate analysis.

CONCLUSION: Patients with secondary APS, those experiencing recurrent thrombosis and exposed to combined antithrombotic treatment, are particularly at risk for bleeding. Patients with thrombocytopenia warrant the most attention as it is both an independent and the strongest risk factor for bleeding that we identified.