How is thromboelastography (TEG) interpreted in clinical practice?

Thromboelastography (TEG) Interpretation in Clinical Practice

Thromboelastography (TEG) provides a comprehensive assessment of the entire coagulation process from initial clot formation through fibrinolysis, allowing for real-time evaluation of hemostatic function that should be interpreted with careful attention to specific parameters and clinical context. 1

Key TEG Parameters and Their Clinical Significance

Primary Parameters

• R time (Reaction time)

  • Measures time from test start to initial fibrin formation (normal: 5-10 minutes)
  • Reflects coagulation factor activity in the intrinsic pathway
  • Prolonged in: factor deficiencies, anticoagulant effect (heparin, warfarin)
  • Shortened in: hypercoagulable states (pregnancy, malignancy)

• K time (Kinetics)

  • Represents speed of clot formation (normal: 1-3 minutes)
  • Prolonged in: hypofibrinogenemia, thrombocytopenia
  • Shortened in: hypercoagulable states

• Alpha angle (α)

  • Reflects fibrinogen function and platelet interaction (normal: 53-72°)
  • Decreased in: hypofibrinogenemia, platelet dysfunction
  • Increased in: hypercoagulability

• MA (Maximum Amplitude)

  • Represents overall clot strength (normal: 50-70 mm)
  • Decreased in: thrombocytopenia, platelet dysfunction, hypofibrinogenemia
  • Increased in: hypercoagulable states
  • Note: Fibrinogen contributes 45% and platelets contribute 55% to overall clot strength 1

• LY30/LY60 (Lysis at 30/60 minutes)

  • Reflects fibrinolytic activity (normal: 0-8%)
  • Increased values indicate hyperfibrinolysis

Common TEG Patterns and Clinical Correlations

1. Hypercoagulable Pattern

   • Shortened R and K times
   • Increased α-angle and MA
   • Common in: pregnancy, malignancy, post-operative states 1

2. Hypocoagulable Pattern

   • Prolonged R and K times
   • Decreased α-angle and MA
   • Common in: factor deficiencies, thrombocytopenia, hemodilution

3. Hyperfibrinolytic Pattern

   • Normal initial parameters with declining amplitude after MA
   • Increased LY30/LY60
   • Common in: trauma with massive hemorrhage, liver disease

4. Anticoagulant Effect

   • Prolonged R time
   • Can detect effects of DOACs with variable sensitivity
   • Heparinase TEG can differentiate heparin effect from coagulopathy 2

Specialized TEG Applications

• Heparinase TEG (hTEG)

  • Contains heparinase to neutralize heparin effect
  • Useful for assessing coagulation in heparinized patients 1

• Functional Fibrinogen TEG (FLEV-TEG)

  • Assesses relative contribution of platelets and fibrin to clot strength 1

• TEG Platelet Mapping (TEG-PM)

  • Evaluates effects of antiplatelet agents 1
  • Note: Standard TEG has limited sensitivity for platelet dysfunction 3

Clinical Applications and Transfusion Guidance

• Trauma and Massive Transfusion

  • Guides component therapy based on specific deficiencies
  • Helps identify hyperfibrinolysis requiring antifibrinolytic therapy

• Liver Disease

  • TEG often reveals rebalanced hemostasis despite abnormal conventional tests
  • TEG-guided transfusion reduces unnecessary blood product use in cirrhotic patients with nonvariceal bleeding 4

• Cardiac Surgery

  • Guides hemostatic management during and after cardiopulmonary bypass
  • Helps differentiate surgical from coagulopathic bleeding

• Obstetrics

  • Can detect pregnancy-associated hypercoagulability
  • Limited sensitivity for detecting hyperfibrinolysis in pregnancy 2

Important Limitations and Pitfalls

• Device Variability and Operator Dependency

  • High coefficients of variance (7.1% to 39.9%) reported for TEG parameters 2, 1
  • Requires proper training and quality control measures

• Insensitivity to Platelet Dysfunction

  • Standard TEG cannot reliably detect platelet function disorders or effects of antiplatelet drugs 3
  • Should be supplemented with specific platelet function tests when needed

• Limited Sensitivity for Hypofibrinolysis

  • May not detect subtle changes in fibrinolysis
  • British Society for Hematology advises that TXA should not be withheld based on normal TEG/ROTEM profile 2

• Sample Processing Issues

  • Delayed analysis and improper collection technique can affect results 1, 5
  • Hemolysis can interfere with TEG results by shortening coagulation times 1

• Interpretation Challenges

  • Results must be interpreted in device-specific context 2
  • Local reference ranges should be established as they are device and manufacturer-specific 2

Best Practices for TEG Implementation

• Establish institution-specific reference ranges
• Implement rigorous quality control measures
• Ensure adequate training of personnel
• Interpret results in clinical context
• Use specialized TEG tests when appropriate (heparinase, functional fibrinogen)
• Recognize that TEG and ROTEM results are not interchangeable due to different reagents and hardware 2

By understanding these parameters and their clinical significance, clinicians can effectively use TEG to guide hemostatic management and transfusion therapy, potentially reducing unnecessary blood product use while improving patient outcomes.