How is a Thromboelastography (TEG) graph interpreted?

Interpreting Thromboelastography (TEG) Graphs

Thromboelastography (TEG) provides a comprehensive real-time assessment of whole blood coagulation and fibrinolysis through a two-dimensional graph that measures various parameters reflecting different aspects of clot formation and breakdown. 1, 2

Key TEG Parameters and Their Interpretation

Clot Formation Parameters

• R time (Reaction time): Measures time to initial fibrin formation (clot initiation)

  • Prolonged R time suggests coagulation factor deficiency or anticoagulant effect 2
  • Shortened R time indicates hypercoagulability 2
  • Normal range: 3.8-9.8 minutes (may vary by institution) 3

• K time (Kinetics): Time from clot initiation to reach 20mm clot width

  • Prolonged K time indicates delayed clot formation 2
  • Shortened K time suggests increased rate of clot formation 2
  • Normal range: 0.7-3.4 minutes (may vary by institution) 3

• Alpha angle (α): Angle between horizontal line and tangent to curve through clot initiation point

  • Increased alpha angle indicates faster clot formation 2
  • Decreased alpha angle suggests slower clot formation 2
  • Normal range: 47.8-77.7 degrees (may vary by institution) 3

• Maximum Amplitude (MA): Represents maximum strength of the clot

  • Decreased MA suggests thrombocytopenia or platelet dysfunction 2
  • Increased MA indicates hypercoagulability 2
  • Normal range: 49.7-72.7 mm (may vary by institution) 3

Fibrinolysis Parameters

• LY30: Percentage of clot lysis 30 minutes after MA is reached

  • Increased LY30 (>7.5%) indicates hyperfibrinolysis and predicts need for massive transfusion 2
  • Decreased LY30 suggests impaired fibrinolysis 2
  • Normal range: -2.3-5.77% (may vary by institution) 3

• Coagulation Index (CI): Composite value reflecting overall coagulation status

  • Normal range: -5.1-3.6 (may vary by institution) 3

Visual Interpretation of the TEG Graph

• The TEG graph displays a characteristic curve with:
  • Initial flat segment representing R time (clot initiation) 1
  • Steepening curve representing K time and alpha angle (clot formation rate) 1
  • Maximum width representing MA (clot strength) 1
  • Potential narrowing after MA representing fibrinolysis 1

Clinical Applications

• TEG effectively detects the hypercoagulable state of pregnancy, showing decreased R and K times with increased MA, alpha angle, and coagulation index 1
• TEG can monitor the effects of anticoagulants, with anticoagulant effect defined as >25% difference between plain and heparinase R time samples 1
• TEG-guided transfusion strategies lead to significantly lower blood component use compared to standard care in patients with coagulopathy 4
• TEG can identify different coagulation patterns in patients with the same factor deficiencies, potentially explaining clinical variability in bleeding disorders 5

Limitations and Pitfalls

• TEG shows high coefficients of variance (7.1-39.9% for TEG parameters), requiring careful interpretation 1
• Results vary between devices and are not interchangeable between TEG and ROTEM systems 1
• Standard TEG is insensitive to antiplatelet agents and cannot reliably detect platelet dysfunction 6
• TEG cannot detect von Willebrand disease or disorders affecting endothelial adherence 2
• Proper training and regular calibration are essential for accurate results 1
• Each institution should determine its own normal values as manufacturer's reference ranges may have limited specificity (81% in one study) 3
• TEG is performed at 37°C and cannot assess effects of hypothermia on coagulation 2

Best Practices for TEG Interpretation

• Use device-specific reference ranges, as results vary between different TEG systems 2
• Consider the clinical context when interpreting results, especially in pregnancy, trauma, or liver disease 2
• For pediatric patients, use age-specific reference values as hemostatic systems change with age 7
• When evaluating platelet function, the k parameter should be used alongside MA for comprehensive assessment 6
• Repeat TEG 15-30 minutes after interventions to assess treatment response 8