After RBC transfusion , platelet reactivity was increased when measured using adenosine diphosphate-induced light transmission aggregometry ( 11.6 % relative increase in maximal platelet aggregation , p = 0.004 ; 10.8 % increase in residual platelet aggregation , p = 0.005 ) and vasodilator-stimulated phosphoprotein platelet reactivity index ( 20.7 % relative increase , p = 0.002 ) , and there was a nonsignificant trend toward an increase in P-selectin expression .