Factor XI: a review of its biochemistry and deficiency.

The biochemistry and physiology of Factor XI have been reviewed. The clinical history of our 25 patients was reviewed and compared with others' experiences. Factor XI deficiency remains enigmatic in that there is no correlation between Factor XI levels and clinical manifestations. Approximately 40 to 50% of all persons lacking Factor XI are of Ashkenazi Jewish extraction, and the remainder are represented by nearly all populations. Persons may be found to lack Factor XI because of evaluation for hemorrhage, evaluation of a prolonged PTT, or through family or other genetic studies. Hemorrhage is not as severe as in patients with hemophilia A or B. Data are presented suggesting that hemorrhage may, in part, be associated with aspirin use.