A method for obtaining a percent aggregation or inhibition of platelets resulting from anti-platelet using a single blood sample is achieved. An assay device is provided. The assay device has multiple channels, each coupled to a common introduction port. A first platelet activator is sensitive to activation pathway targeted by the anti-platelet drug. A second platelet activator is insensitive to the activation pathway targeted by the anti-platelet drug. An anti-coagulated sample is introduced simultaneously to the first and second channels. A level of platelet aggregation is simultaneously made in both channels.