VON-WILLEBRAND-FACTOR ANTIGEN AND FACTOR-XI ACTIVITY LEVELS AS PREDICTORS OF BLEEDING TENDENCY IN ISRAELI PATIENTS WITH VON WILLEBRANDS DISEASE

Previous preliminary data and case reports have suggested an associati on of von Willebrand's disease (vWD) with factor XI deficiency and pla telet abnormalities. We have analyzed the prevalence of factor XI defi ciency and thrombocytopathy in a cohort of Israeli patients with VWD. Decreased factor XI levels (<67 U/dl) were documented in 35 of 63 (56% ) vWD subjects; factor XI levels were <30 U/dl in five of 60 (8%). A s ignificant decline in ADP-induced platelet aggregation (<30% of contro l) was found in 48% of vWD patients. Likewise, epinephrine-induced agg regation was reduced in 41%, and collagen-induced aggregation was decr eased in 7% of vWD patients. Logistic regression analysis showed that while Ivy bleeding time, ristocetin cofactor, and ristocetin-induced p latelet aggregation did not predict bleeding, both von Willebrand fact or antigen and factor XI activity levels predict bleeding in patients with vWD. These findings suggest that mild factor XI deficiency and th rombocytopathy are common in Israeli subjects with vWD and that associ ated factor XI deficiency can result in clinical bleeding in these pat ients.