[Factor XI deficiency: do patients with hemorrhagic diathesis also have hemostasis defects?]

It is well known that the extent of bleeding in patients with a deficiency of factor XI does not parallel the residual factor activity. Therefore, additional hemostatic aspects must be taken into consideration. 27 patients of 18 different families--6 with severe (FXI < 0.01 to 0.09 U/ml) and 21 with moderate (FXI 0.20 to 0.252 U/ml) factor XI deficiency--were reinvestigated regarding hemostasis including bleeding time and platelet function. 16 had an enhanced bleeding tendency, while the others--including 3 with severe FXI deficiency of < 0.01 U/ml--never suffered from bleeding complications despite delicate surgery in some. All 16 of the symptomatic patients had, besides the reduction of factor XI activity to various extents, an additional hemostatic defect: 3 had a moderate alpha/delta storage pool detect of the platelets, 11 a platelet anomaly mainly characterized by reduced ADP aggregation and 2 an isolated prolonged bleeding time of unknown cause. Synthesis of platelet thromboxane was unimpaired in all patients as tested by formation of malondialdehyde after stimulation with N-ethyl maleimide. Hence, in patients with a known factor XI deficiency diagnostic and prophylactic measures before surgery should concentrate on such additional findings. Preoperative administration of desmopressin, and not replacement of factor XI, will be the treatment of choice in these cases.