What is Thromboelastography?

Thromboelastography, commonly known as TEG, is a medical test that provides a comprehensive analysis of a patient's hemostasis or coagulation system. It measures the kinetics of clot formation and lysis under low shear stress conditions. TEG gives invaluable insight into a patient’s coagulation process that cannot be gained through routine coagulation tests like prothrombin time (PT) and activated partial thromboplastin time (aPTT).

TEG was developed in the 1940s by Dr. H. Hartert while investigating why blood took a variable amount of time to clot. The first clinical TEG analyzer was developed in the late 1980s by Kevin Messmore and Nick Ferrara. Today, TEG is widely used in surgical procedures, trauma, liver disease, cardiac surgery and massive transfusions to monitor coagulation status and guide blood product administration.

How does TEG work?

A TEG analysis requires just 340 microliters of whole blood. The blood sample is placed in a heated cup housed within the TEG analyzer. A rotating pin is then suspended in the cup and oscillation is initiated. As the blood sample clots, strands called fibrin are formed, connecting the pin to the cup walls. The machine precisely tracks and records the movement of the pin throughout clot formation and lysis.

Graphical interpretation of TEG results

The kinetic data generated by TEG is displayed as a waveform tracing on the TEG analyzer screen. Different parameters of the tracing provide comprehensive information about the various stages of coagulation:

- Reaction Time (R): Time taken for initial fibrin formation. Indicates coagulation factor function.

- Kinetics (K): Rate of fibrin build up, intersection of rate of clot strengthening. Reflects clot strengthening under thrombin generation.

- Angle (α): Determined by rate of clot strengthening over the first 20 minutes. Index of intrinsic coagulation pathway function and fibrinogen function.

- Maximum Amplitude (MA): Reflects clot strength, maximum dynamic strength achieved. Governed by platelet number and function.

- Lysis 30 (Ly30): Percentage reduction in amplitude at 30 minutes post MA. Indicates fibrinolytic activation.

Advantages of TEG over routine coagulation tests

Some key advantages of TEG over tests like PT, aPTT and platelet count include:

- TEG is a more global test reflecting the interactions between platelets, coagulation factors and fibrinolysis throughout the entire clotting process.

- It provides both qualitative and quantitative assessment of clot strength through various parameters rather than just one value.

- TEG directly assesses clot strength (MA) which standard tests cannot. This is especially helpful in trauma and surgery where thrombin generation and platelet function are crucial.

- TEG results are available within 10-15 minutes allowing timely diagnosis and treatment, unlike standard tests requiring 30-45 minutes.

- It is highly sensitive in detecting coagulopathies commonly encountered in liver disease, massive transfusions and cardiac surgery.

Clinical applications of TEG

TEG has transformational applications in guiding hemostatic management in various clinical settings:

- Trauma: Rapidly detects hemorrhagic tendencies and guides tranexamic acid, FFP, platelets and cryoprecipitate use.

- Liver disease: Distinguishes between hypercoagulable and hypocoagulable states, essential in invasive procedures.

- Cardiac surgery: Pinpoints acquired coagulopathies from hemodilution, hypothermia and fibrinolysis; targeted factor concentrates lower bleeding risks.

- Obstetrics: Monitors hypercoagulability in preeclampsia/eclampsia; guides management of abnormal bleeding during delivery.

- Massive transfusions: Optimizes transfusion thresholds by precisely determining coagulation factor and platelet requirements on a patient-specific basis.

TEG provides a global, whole blood assay of hemostasis that cannot be reproduced through routine blood tests alone. Its use helps optimize blood product transfusion, reduces healthcare costs and improves clinical outcomes. As clinical experience grows, TEG is emerging as the gold standard for guiding hemostatic management in an increasing variety of surgical and medical conditions.

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