Apparatus and method for evaluating platelet functionality of a blood sample. A cartridge includes a plurality of test cells. Each cell receives an aliquot part of a blood sample. A measured amount of clotting reagent is provided in each cell. A measured amount of platelet activation reagent is provided in each cell, the amount of such reagent in each cell differing from the amount of such reagent in each other cell. The relative clotting times of the aliquot samples in the cells are determinative of the platelet functionality of the blood sample.