New Hemostasis Tests Evaluation of the Overall Coagulation Potential by the Thrombin Generation Assay

Test for the evaluation of the overall coagulation potential in plasma. Given the central role of thrombin in blood clotting, the tendency of a plasma sample to generate thrombin might contain useful information about thrombotic or haemorrhagic risk. In this presentation I will talk about the thrombin generation (TG) assay by the Calibrated Automated Thrombogram (CAT), developed in Maastricht by Dr. Hemker. In this assay, the formation of thrombin in full plasma is induced by a mixture of TF, phospholipids (PL) and CaCl2, and it is monitored by measuring the fluorescence signal generated by a fluorogenic thrombin substrate. The result of the test is a thrombin generation curve (thrombogram) characterized by the following parameters: a lag phase (initiation), a propagation phase, which reaches the maximum at the peak of the curve , and the termination phase due to the inhibition of thrombin activity by plasma protease inhibitors. The area under the curve, i.e. the endogenous thrombin potential (ETP), represents the total amount of thrombin formed. Each parameter is dependent on specific procoagulant/ anticoagulant proteins. The analytical conditions of the test can be modified to increase the sensitivity of the assay by varying the TF, PL and substrate concentrations. The pre-analytical conditions of the test (i.e. blood withdrawal and plasma preparation) are very important to achieve reliable results. An increased ETP has been described in prothrombotic conditions, while reduced ETP was found in hemorrhagic disorders. When the test is performed in the presence of activated Protein C (APC) (i.e. ETP-based APC resistance test), the APC-resistant phenotype, secondary or not to FVL, can be detected. With this test, an acquired APC resistance has been described in women on oral contraceptives or hormonal replacement therapy, in patients with lupus anticoagulant and in cancer.