The perils of inhibiting deficient factors

Essentials Anticoagulation in patients with factor X deficiency is an evidence‐poor area. A patient with factor X deficiency was anticoagulated with warfarin followed by rivaroxaban. Warfarin may be a safer anticoagulant option than rivaroxaban in hereditary factor X deficiency. A baseline coagulation screen should be performed prior to commencement of anticoagulation.Summary We report a case of a previously undiagnosed factor X deficiency in an 83‐year‐old man who had no previous bleeding history despite multiple hemostatic challenges. He was anticoagulated with warfarin for atrial fibrillation without bleeding complications; however, major hemorrhage occurred soon after a switch to rivaroxaban.