Advanced, Basic Sciences
Thromboelastography (TEG) is a point of care method of testing the efficiency of coagulation of whole blood, and provides a global assessment of hemostatic function. It is especially useful as a guide for goal-directed transfusion therapy in major procedures with large expectant blood loss (ex. liver transplantation, cardiac, trauma, major obstetric hemorrhage), and has been shown to reduce total blood product usage.
TEG assesses the strength of clot in a blood sample by measuring the amount of resistance it produces. The blood sample is placed in a cup, after which a torsion pin is submerged within the sample. The cup then oscillates against the torsion pin, and the amplitude of pin motion is directly proportional to the strength of the clot. This can be plotted over time and give valuable information about thrombus formation, platelet function, and fibrinolysis. (see image and table)
In addition to these basic parameters, TEG can be modified with various reagents to further isolate the cause of coagulopathy:
- Heparinase – an enzyme that breaks down heparin can help assess for abnormal coagulation prior to heparin reversal with protamine, as is often the case with prolonged cardiopulmonary bypass, deep hypothermia, and use of ventricular assist devices.
- C7E3 Fab (Reopro) – a platelet inhibitor that eliminates any platelet contribution to thrombus strength. The maximum amplitude would become a function of fibrinogen activity.
Of note, while TEG and ROTEM (rotational thromboelastometry) are conceptually very similar, they are two separate proprietary systems. Differences in equipment and clot activators use means that the two systems have different reference values and test measurements cannot be directly compared.