How do you interpret a Thromboelastography (TEG) result?

Interpreting Thromboelastography (TEG)

Thromboelastography (TEG) provides a comprehensive real-time assessment of whole blood coagulation that can replace conventional coagulation tests in emergency settings, with results available within minutes compared to conventional tests that take up to 48 minutes. 1, 2

Key TEG Parameters and Their Interpretation

Clot Formation Parameters

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

  • Normal range: 3.8-9.8 minutes 3
  • Prolonged R time suggests coagulation factor deficiency or anticoagulant effect 4
  • Shortened R time indicates hypercoagulability 4

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

  • Normal range: 0.7-3.4 minutes 3
  • Prolonged K time indicates delayed clot formation 4
  • Shortened K time suggests increased rate of clot formation 4

• Alpha angle (α): Measures speed of fibrin buildup and cross-linking

  • Normal range: 47.8-77.7 degrees 3
  • Increased angle indicates faster clot formation 4
  • Decreased angle suggests slower clot formation 4

Clot Strength Parameters

• Maximum Amplitude (MA): Represents maximum strength of the clot
  • Normal range: 49.7-72.7 mm 3
  • Decreased MA suggests thrombocytopenia or platelet dysfunction 4
  • Increased MA indicates hypercoagulability 4
  • MA correlates better with platelet count than conventional tests for predicting platelet transfusion needs 1, 2

Fibrinolysis Parameters

• LY30: Percentage of clot lysis 30 minutes after MA is reached
  • Normal range: -2.3-5.77% 3
  • Increased LY30 (>7.5%) indicates hyperfibrinolysis and predicts need for massive transfusion 4, 1
  • Decreased LY30 suggests impaired fibrinolysis 4

Types of TEG Assays and Their Applications

• Standard TEG (Kaolin or Celite): Evaluates intrinsic pathway coagulation 4
• Rapid TEG (rTEG): Uses tissue factor plus kaolin to activate both intrinsic and extrinsic pathways, providing faster results 4, 2
• Heparinase TEG (hTEG): Assesses the effect of heparin on coagulation 4
• TEG Platelet Mapping (TEG-PM): Evaluates platelet function and effects of antiplatelet agents 4
• Functional Fibrinogen TEG (FLEV-TEG): Isolates fibrin contribution to clot strength 4

Clinical Applications

• Trauma: TEG predicts blood component requirements better than conventional tests

  • ACT >128 predicts massive transfusion in first 6 hours (odds ratio 5.15) 2
  • ACT <105 predicts patients who won't need transfusions (odds ratio 2.80) 2
  • Alpha angle predicts massive RBC transfusion better than PT/aPTT or INR 1

• Obstetrics: TEG reflects hypercoagulable state of pregnancy

  • Shows progressive resolution of hypercoagulability postpartum 4
  • Can detect coagulation changes during cesarean delivery 4

• Perioperative Management: Guides transfusion therapy during cardiac and hepatic surgeries 5, 6

Limitations and Pitfalls

• Insensitivity to certain conditions: TEG cannot detect von Willebrand disease or disorders affecting endothelial adherence 4

• Limited platelet function assessment: Standard TEG is insensitive to antiplatelet agents and cannot reliably detect platelet dysfunction 4

• Variable results: TEG shows high coefficients of variance (7.1-39.9% for TEG parameters) 4

  • Results vary between devices and are not interchangeable between TEG and ROTEM 4
  • Proper training and regular calibration are essential 4

• Hematocrit influence: Anemia can paradoxically show hypercoagulable TEG results due to decreased blood viscosity 4

• Temperature effects: TEG is performed at 37°C and cannot assess effects of hypothermia 4

• Reference range variability: Manufacturer's normal values may not apply to all populations

  • Institution-specific normal ranges are recommended 3
  • Gender differences exist - women typically show more hypercoagulable profiles than men 3

Best Practices for TEG Interpretation

• Use device-specific reference ranges, as results vary between different TEG systems 4, 3
• Consider the clinical context when interpreting results, especially in pregnancy, trauma, or liver disease 4, 1
• Recognize that TEG results correlate with but do not replace conventional coagulation tests 2
• Understand that TEG provides a global assessment of hemostasis but has limitations in detecting specific coagulation disorders 4
• For fibrinolysis assessment, recognize that TEG may have limited sensitivity in detecting hypofibrinolysis 4