Thromboelastography (TEG) is a point-of-care test that provides a comprehensive assessment of a patient’s hemostatic system. It measures the dynamics of clot formation and breakdown over time, providing a picture of clot strength and structure. This allows clinicians to better understand a patient’s clotting tendencies and bleeding risks.
What is TEG?
TEG uses a pin and cup apparatus to measure the physical properties of clot formation and lysis. A small sample of whole blood is placed in a cup containing a pin. As the sample clots, it connects the pin to the cup. Sensors in the cup then track the pin movement over time and record data reflecting different stages of clotting. This data is presented as a thromboelastogram tracing that can be used to assess various aspects of hemostasis.
Stages of Clotting
The Thromboelastogram shows five key stages of clot development:
R Time – measures the reaction time or time to initial fibrin formation and clot strength. A prolonged R time indicates a coagulation factor deficiency.
K Time – measures the time needed to achieve a specific clot firmness. Prolonged K time suggests a platelet dysfunction or inhibition.
Angle – reflects the speed of clot buildup and strengthening. A decreased angle implies impaired thrombin generation or reduced fibrin production rates.
Maximum Amplitude (MA) – indicates ultimate clot strength. A reduced MA points to a platelet dysfunction or low fibrinogen level.
Lysis 30 – measures clot lysis or breakdown at 30 minutes. Increased lysis denotes a hyperfibrinolysis or excessive clot breakdown.
TEG allows clinicians to parse out where in the coagulation-fibrinolysis process an abnormality may lie. This provides a more comprehensive evaluation than conventional clotting tests.
Clinical Uses of TEG
TEG sees wide use in surgical specialties like cardiac, liver transplant and trauma surgery to guide blood product transfusion. Some ways it aids clinical decision making:
– Assessing coagulation status in patients with bleeding or those at high risk of bleeding preoperatively.
– Guiding transfusions of plasma, platelets, cryoprecipitate or fibrinogen concentrate intraoperatively based on specific clotting deficits detected.
– Monitoring for hypercoagulability and thrombosis risks in critically ill patients.
– Evaluating abnormal bleeding or thrombosis in hematological disorders.
– Detecting coagulopathy in obstetric hemorrhage and guiding treatment.
– Monitoring anticoagulant effects during cardiopulmonary bypass or extracorporeal support.
TEG Advantages
TEG offers several advantages over standard coagulation tests:
– Whole blood-based testing accounts for cell interactions crucial to hemostasis.
– Kinetically monitors clotting over time rather than providing a static view.
– Detects hyper and hypocoagulable states simultaneously due to comprehensive profile.
– Quick turnaround time of under an hour allows goal-directed therapy during surgeries.
– Less sample volume required than multiple individual lab tests.
– Bedside availability facilitates urgent clinical decisions and intraoperative guidance.
Limitations of TEG include operator dependence, lack of standardization between instruments, and inability to identify specific clotting factor deficiencies. However, the global picture it constructs of hemostasis aids management of complex bleeding patients.
Future Directions
Point-of-care hemostasis assays continue getting more widespread as their clinical value is recognized. Future directions include:
– Automating interpretation through computer software to minimize variability.
– Integrating viscoelastic testing into hematology analyzers and lab environments.
– Developing affinity reagents to identify specific coagulation factor abnormalities.
– Applying TEG principles for non-surgical conditions involving hemostasis disorders.
– Utilizing quantitative TEG parameters to establish standardized transfusion algorithms.
– Studying outcomes data on TEG-guided resuscitation versus standard practice.
– Developing portable handheld viscoelastic testing devices for use in prehospital settings.
– Incorporating new biomarkers and genetic tests into multi-parameter hemostasis profiles.
Thromboelastography provides a global assessment of hemostasis that has significantly enhanced transfusion management for bleeding patients. The kinetic view it offers of whole blood clotting dynamics aids better understanding and treatment of coagulopathy. Its clinical utility continues expanding as technology evolves to address current limitations. TEG remains a valuable point-of-care tool for evaluating and normalizing hemostasis.
