LAUSR

The bleeding phenotype of FXI deficiency is unpredictable. Bleeding is usually mild, and mostly occurs after injury. Although FXI deficiency renders antithrombotic protection, some patients might eventually develop thrombosis or atrial fibrillation, requiring anticoagulant therapy. There is almost no evidence on the bleeding risk in this scenario. Our retrospective study of 269 Caucasian FXI-deficient subjects (1995-2021) identified 15 cases requiring anticoagulation. They harbored eight different F11 variants, mainly in heterozygosis (one case was homozygote) and had mild-moderate deficiency (FXI:C:20-70%). Two subjects (13.3%) had bleeding history before anticoagulation. Atrial fibrillation was the main indication (12/15,80%). Fourteen patients started therapy with vitamin K antagonists (VKA), but four were on direct oral anticoagulants (DOACs) at the end of follow-up. Over more than 1000 months of anticoagulation, two mild bleeding episodes in two patients (13.3%,95%CI:3.7-37.9%) were recorded. No major/fatal events were reported. "Pre-post" bleeding localization and severity did not change despite treatment. On VKA, drug dosing and management were also standard, unaltered by FXI deficiency. We provide the largest description of anticoagulant use in FXI deficiency, and the first cases receiving DOACs. While further studies are needed, our observations suggest that moderate FXI deficiency does not interfere with anticoagulant management nor bleeding risk.