Ongoing risk of thrombosis with factor XI concentrate: 5 years experience in two centres.

INTRODUCTION: Factor XI (FXI) deficiency is the commonest of the rare bleeding disorders, affecting 2079 individuals in the United Kingdom. Treatment options for bleeding or surgery include antifibrinolytics, fresh frozen plasma or plasma-derived (pd) FXI concentrates. There were a number of reports of thrombosis following treatment with FXI concentrates prior to changes in their manufacturing processes made in the mid-1990's.

AIMS: The aim of the study was to determine the occurrence of adverse events (haemorrhagic and thrombotic) following usage of pd-FXI concentrates at two large UK haemophilia centres. Retrospective chart review of all consecutively treated patients with BPL Factor XI(®) or Hemoleven(®) over a 5-year period (11/06-11/11) was performed.

RESULTS: Twenty-nine patients (median age = 57.1 years) received treatment over 64 treatment episodes (surgery = 56, bleeding = 5, other = 3), using 126 000 U of concentrate. Median baseline FXI:C was 9 U dL(-1) (range = <1-51), with 21 having severe and eight partial deficiency. BPL Factor XI(®) was used in 39 episodes (79 110 U) and Hemoleven(®) 25 episodes (46 890 U). There were six clinically significant bleeding events, managed either with a single additional dose of FXI concentrate (n = 4) or requiring no further intervention (n = 2). One patient required blood transfusion and one oral iron replacement. Two thrombotic events (transient ischaemic attack and pulmonary emboli), occurred in two patients with severe FXI deficiency, despite cautious FXI concentrate usage in the perioperative period.

CONCLUSIONS: FXI concentrate use is efficacious and safe in the majority of cases although physicians should remain mindful of the possibility of thrombotic complications.