Thromboelastography (TEG): Point-of-Care Coagulation Assessment
TEG is a point-of-care viscoelastic test that uses whole blood to assess the entire coagulation process in real-time, from initial clot formation through fibrinolysis, providing quantitative results within 30 minutes to guide targeted blood product therapy. 1
How TEG Works
TEG analyzes coagulation by placing whole blood in an oscillating cup with a free-floating pin that senses changes as blood clots and breaks down. The device generates a real-time two-dimensional graph (TEMogram) that reflects the dynamic process of hemostasis. 1
Key TEG Parameters
The test measures five critical components of coagulation 1:
- R time (Reaction time): Time to initial clot formation - reflects clotting factor function
- K time (Kinetics): Time from clot initiation to reach 20mm clot width - reflects fibrinogen function and clot kinetics
- Alpha angle (α): Angle of clot formation curve - reflects speed of clot strengthening
- MA (Maximum Amplitude): Maximum clot strength measured in mm - reflects platelet function and fibrinogen contribution (platelets contribute ~55%, fibrinogen ~45%)
- Ly30/Ly60: Percentage of clot lysis at 30/60 minutes - detects fibrinolysis
Types of TEG Assays
Different reagents target specific coagulation components 1:
- Standard TEG (kaolin/celite): Evaluates intrinsic pathway and overall hemodynamic changes
- Rapid TEG (tissue factor + kaolin): Faster results by activating both intrinsic and extrinsic pathways
- Heparinase TEG: Assesses heparin's effect on coagulation
- TEG Platelet Mapping: Evaluates platelet function and antiplatelet drug effects
- Functional Fibrinogen TEG: Isolates fibrinogen's contribution to clot strength
Clinical Applications for Guiding Therapy
Established Uses with Strong Evidence
TEG-guided transfusion protocols reduce blood product utilization and improve patient outcomes in cardiac surgery, liver transplantation, and trauma settings. 2
In cardiac and liver surgery, TEG-guided therapy significantly reduces:
- Platelet transfusions (p=0.004)
- Plasma transfusions (p<0.001)
- Operating room length of stay (p=0.005)
- ICU length of stay (p=0.04)
- Bleeding rates (p=0.002)
- Mortality remains comparable, indicating safety 2
In emergency/trauma resuscitation, TEG-guided protocols demonstrate:
- Reduced mortality (p=0.049)
- Decreased platelet and plasma transfusions
- Increased ventilator-free days 2
In medical ICU settings, TEG implementation associates with:
- Significantly reduced plasma administration (658.3 mL vs 410.8 mL per patient, p<0.001)
- No increase in mortality or hospital length of stay 3
Specific Clinical Scenarios
Postpartum hemorrhage: ROTEM (TEG's counterpart) may guide transfusion therapy, though only two randomized controlled trials exist in obstetrics, limiting robust evidence. 1
Hypercoagulable state detection: TEG reliably detects pregnancy-associated hypercoagulability and may predict thromboembolic risk in various populations. 1, 4
Antiplatelet therapy monitoring: TEG Platelet Mapping assesses antiplatelet drug effects, useful before procedures like carotid stenting. 4
Heparin monitoring: Heparinase TEG differentiates heparin effect from intrinsic coagulopathy during extracorporeal membrane oxygenation (ECMO) or cardiopulmonary bypass. 5
Advantages Over Standard Coagulation Tests
- Rapid turnaround: Results in <30 minutes vs hours for conventional tests 6
- Whole blood analysis: Evaluates cellular and plasma components together, reflecting in vivo conditions
- Point-of-care capability: Bedside testing enables immediate clinical decisions
- Detects hyperfibrinolysis: Standard tests cannot identify this critical bleeding cause 5
- Small sample volume: Particularly advantageous in pediatrics
- Monitors factor XIII activity: Not routinely assessed by standard tests 5
Important Limitations and Caveats
High coefficient of variation: TEG has greater test-to-test variability than standard coagulation assays, requiring careful interpretation. 5
Lack of standardization: Methodologies vary between institutions, limiting generalizability of specific cutoff values. 1, 5
Specimen stability issues: Native whole blood samples have limited stability, requiring prompt analysis. 5
Age-specific reference ranges: Pediatric patients, especially newborns, require different normal values than adults. 5
Limited RCT evidence in some settings: While cardiac surgery and trauma have strong evidence, other applications (obstetrics, vascular surgery) lack robust randomized trials. 1, 4
Cost considerations: TEG testing is more expensive than standard coagulation assays, though may offset costs through reduced transfusions. 7
Practical Implementation Strategy
When using TEG to guide therapy:
- Establish institution-specific protocols: Define transfusion thresholds based on TEG parameters for your patient population
- Interpret in clinical context: TEG abnormalities must correlate with clinical bleeding; don't treat numbers alone
- Use targeted component therapy:
- Low MA → platelets or cryoprecipitate (use functional fibrinogen TEG to differentiate)
- Prolonged R/K → plasma or specific factor concentrates
- Elevated Ly30 → antifibrinolytics (tranexamic acid)
- Recheck after intervention: Serial TEG guides adequacy of resuscitation
- Consider fluid effects: Colloid vs crystalloid preloading affects TEG parameters differently 1
Critical pitfall: TEG reflects coagulation at the time and temperature of testing. Hypothermia, acidosis, and hemodilution in the actual patient may worsen coagulopathy beyond what TEG predicts. Correct these physiologic derangements concurrently.