How do you interpret a Thromboelastography (TEG) score?

How to Interpret a Thromboelastography (TEG) Score

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. 1 Understanding TEG parameters is essential for accurate clinical decision-making in situations involving coagulopathy.

Key TEG Parameters and Their Interpretation

Initial Clot Formation 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 R: factor deficiency, anticoagulant effect
  • Shortened R: hypercoagulable state 1, 2

• K time (Kinetics)

  • Time from beginning of clot formation until 20mm amplitude is reached (normal: 1-3 minutes)
  • Represents speed of clot formation
  • Prolonged K: hypofibrinogenemia, thrombocytopenia
  • Shortened K: hypercoagulable state 1, 3

• Alpha angle (α)

  • Rate of clot formation (normal: 53-72°)
  • Reflects fibrinogen function and platelet interaction
  • Decreased angle: hypofibrinogenemia or platelet dysfunction
  • Increased angle: hypercoagulability 1, 3

Clot Strength Parameters

• MA (Maximum Amplitude)
  • Maximum strength of the clot (normal: 50-70mm)
  • Represents platelet function and fibrinogen contribution
  • Decreased MA: thrombocytopenia, platelet dysfunction, hypofibrinogenemia
  • Increased MA: hypercoagulable state 1, 4
  • Studies show fibrinogen contributes 45% and platelets contribute 55% to overall clot strength 1

Clot Stability Parameters

• LY30/LY60 (Lysis at 30/60 minutes)

  • Percentage of clot lysed at 30 or 60 minutes after MA
  • Reflects fibrinolytic activity
  • Increased values (>8%): hyperfibrinolysis
  • Decreased values: impaired fibrinolysis 1

• CI (Coagulation Index)

  • Overall assessment of coagulation status
  • Combines R, K, MA, and α-angle
  • Negative values: hypocoagulable state
  • Positive values: hypercoagulable state 5, 3

Specialized TEG Assays

Modified TEG Tests

• Heparinase TEG (hTEG)

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

• Functional Fibrinogen TEG (FLEV-TEG)

  • Uses GPIIb/IIIa platelet inhibitor to isolate fibrin contribution
  • Assesses relative contribution of platelets and fibrin to clot strength 1, 6

• TEG Platelet Mapping (TEG-PM)

  • Uses ADP or arachidonic acid to assess platelet function
  • Evaluates effects of antiplatelet agents 1

• Rapid TEG (rTEG)

  • Uses tissue factor plus kaolin to activate both intrinsic and extrinsic pathways
  • Provides faster results (within 5-15 minutes) compared to standard TEG
  • ACT (Activated Clotting Time) replaces R time 2

Clinical Applications and Interpretation Pearls

Hypercoagulable States

• Pattern: Shortened R and K times, increased α-angle and MA
• Common in pregnancy, malignancy, and post-operative states 1
• MA-R ratio (MA divided by R time) can be useful for identifying hypercoagulable patients at risk of thrombosis 4

Hypocoagulable States

• Pattern: Prolonged R and K times, decreased α-angle and MA
• Seen in factor deficiencies, thrombocytopenia, and hemodilution 3

Fibrinolysis

• Pattern: Normal initial parameters with declining amplitude after MA
• Increased LY30/60 values indicate hyperfibrinolysis 1

Common Pitfalls in TEG Interpretation

1. Sample handling issues

   • Delayed analysis can affect results
   • Proper collection technique is essential for accurate results

2. Device variability

   • Results may vary between different TEG devices
   • Reference ranges are device-specific 1

3. Operator dependency

   • Requires proper training and calibration
   • High coefficients of variance (7.1% to 39.9%) have been reported 1

4. Hemolysis interference

   • Hemolysis can affect results, particularly in ECMO patients
   • Free hemoglobin can shorten coagulation times 7

5. Limited sensitivity for platelet dysfunction

   • TEG may not provide a comprehensive assessment of platelet function
   • Should be supplemented with other platelet function tests when needed 6

TEG vs. Conventional Coagulation Tests

• TEG results correlate with conventional tests but provide more comprehensive information
• R time correlates with PT/INR and APTT
• MA correlates with platelet count and fibrinogen levels
• TEG provides faster results (5-15 minutes) compared to conventional tests (48 minutes) 2, 3

By understanding these parameters and their clinical significance, clinicians can effectively utilize TEG to guide transfusion therapy, monitor anticoagulation, and assess coagulation status in various clinical scenarios.