( 1 ) PF4/H antibody-positive patients suffered a significantly higher incidence of thrombosis than those who were antibody-negative ; ( 2 ) PF4/H antibody-positive patients who survived a thrombosis manifested a significantly longer bleeding time and decreased maximum percentage of platelet aggregation inhibition ; ( 3 ) aspirin and clopidogrel decreased the incidence of thrombosis in PF4/H antibody-positive patients by inhibiting platelet activation .