Effect of dextran 70 on factor VIII and platelet function in von Willebrand's disease.

Dextran given intravenously to two patients with mild von Willebrand's disease and two healthy controls impaired the factor VIII properties measured, i.e. it decreased the factor VIII-related antigen and the ristocetin co-factor activity. In the patients the variables fell from borderline to abnormally low levels accompanied by a prolongation of the bleeding time. Infusion of factor VIII concentrate reversed the dextran-induced impairment of factor VIII and the prolonged bleeding time. The findings lend support to the view that dextran induces a defective platelet function in vivo by interfering with the factor VIII molecular complex. They also show that patients with von Willebrand's disease should not be given dextran as it might potentiate their bleeding diathesis.