An improved apparatus and method for evaluating platelet functionality of a blood sample. The apparatus includes a plurality of test cells. Each of the cells includes a platelet function restoration agent, an anticoagulant agent, and a clotting reagent. At least one of the cells also includes a platelet activating agent. The clotting time is determined for each of the aliquot portions, and the relative clotting times of the aliquot portions in the cells are determinative of the platelet functionality of the sample. The method includes the steps of combining a platelet function restoration agent, an anticoagulant agent, a platelet activating agent, and the sample of blood to be tested to form a test mixture. The platelets of the sample are activated by adding a clotting reagent to the test mixture at the start of the activated clotting time test, and the activated clotting time test is terminated upon detecting a predetermined change in a property of the test mixture. The activated clotting time of the sample of blood is calculated based on the elapsed time.