Recurrent venous thromboembolic disease and factor XI concentrate in a patient with severe factor XI deficiency, chronic myelomonocytic leukaemia, factor V Leiden and heterozygous plasminogen deficiency.

There are increasing concerns about the potential thrombogenic risks associated with the use of factor XI concentrates. We describe the case of a 49 year-old man with chronic myelomonocytic leukaemia and severe factor XI deficiency (< 1 u/dl), in whom the use of factor XI concentrate appeared to be associated with the development of venous thromboembolic disease. Subsequent investigations revealed the presence of both the factor V Leiden abnormality and heterozygous plasminogen deficiency. This case highlights the risks associated with the use of factor XI concentrates and suggests that these risks may be further increased in patients with an inherited or acquired prothrombotic abnormality or an underlying malignancy. Prothrombotic screening of patients with severe factor XI deficiency may be indicated particularly in younger patients in whom treatment with factor XI concentrates is a possibility.