Thromboelastography (TEG) is normally used in surgery to assess the quality of clot formation. However, a modified TEG method can be used to assess an individual's response to antiplatelet therapy.
Agonists are added to a whole blood sample to begin the thrombotic process. The instrument has a pin attached to a tension wire which, when lowered into a rotating cup, causes thrombi formation. The thrombi create a tension on the wire, which is measured in a curve plot by the analyzer. When testing for clopidogrel response, the test is run with ADP-, fibrin-, and kaolin-coated cups.
Evaluations of patient results are compared to the manufacturer's reagents for each system. Typically, a lack of inhibition of thrombus formation would indicate resistance to clopidogrel. A cut-off value that determines non-responsiveness (resistance) to antiplatelet therapy must be established or verified by the testing laboratory.