THE REDUCTION OF LARGE VON-WILLEBRAND-FACTOR MULTIMERS IN PLASMA IN ESSENTIAL THROMBOCYTHEMIA IS RELATED TO THE PLATELET COUNT

We have investigated the relationship between platelet count and large VWF (von Willebrand factor) multimers in the plasma of 36 patients wi th essential thrombocythaemia (ET) and 20 patients with reactive throm bocytosis (RT). In both ET and RT patients an inverse relationship cou ld be established between platelet count and large VWF multimers in pl asma as well in relatively decreased ristocetin cofactor/von Willebran d factor antigen and collagen binding activity/von Willebrand factor a ntigen ratios. A normalization of the platelet count was accompanied b y restoration of a normal plasma VWF multimeric distribution. Our data suggest that increasing numbers of platelets circulating in blood res ult in increased removal of large VWF multimers from plasma.