How do you interpret a Thromboelastography (TEG) study?

Interpreting Thromboelastography (TEG) Studies

Thromboelastography (TEG) should be interpreted with caution, recognizing its significant limitations in detecting certain coagulation disorders while understanding the clinical significance of each parameter to guide appropriate interventions. 1, 2

Key TEG Parameters and Their Clinical Significance

Primary Parameters

• R time (Reaction time)

  • Measures time from test start to initial fibrin formation
  • Prolonged in factor deficiency or anticoagulant effect
  • Shortened in hypercoagulable states
  • Normal range: 3.8-9.8 minutes 3

• K time (Kinetics)

  • Represents speed of clot formation
  • Prolonged in hypofibrinogenemia or thrombocytopenia
  • Shortened in hypercoagulable states
  • Normal range: 0.7-3.4 minutes 3

• Alpha angle (α)

  • Reflects fibrinogen function and platelet interaction
  • Decreased in hypofibrinogenemia or platelet dysfunction
  • Increased in hypercoagulability
  • Normal range: 47.8-77.7 degrees 3

• MA (Maximum Amplitude)

  • Represents overall clot strength (platelet function and fibrinogen contribution)
  • Decreased in thrombocytopenia, platelet dysfunction, or hypofibrinogenemia
  • Increased in hypercoagulable states
  • Normal range: 49.7-72.7 mm 3

• LY30/LY60 (Lysis at 30/60 minutes)

  • Reflects fibrinolytic activity
  • Increased values indicate hyperfibrinolysis
  • Normal range for LY30: -2.3-5.77% 3

Critical Limitations to Consider

1. Cannot detect platelet function disorders

   • Standard TEG is insensitive to antiplatelet agents or platelet inhibition 1, 4
   • Cannot reliably detect von Willebrand disease or disorders affecting endothelial adhesion 1
   • Should be supplemented with specific platelet function tests when needed 2, 4

2. Variable reliability

   • High coefficients of variance (7.1% to 39.9%) for TEG parameters 1, 2
   • Results must be interpreted in device-specific context 1
   • Manufacturer's normal values may incorrectly identify healthy individuals as coagulopathic (81% specificity) 3

3. Limited detection of fibrinolysis

   • Debate regarding sensitivity in detecting hypo- or hyperfibrinolysis 1
   • The British Society for Hematology advises that tranexamic acid should not be withheld based solely on normal TEG profile 1, 2

4. Technical factors affecting results

   • Hemolysis can interfere with results 2
   • Delayed analysis and improper collection technique affect accuracy 2
   • Operator dependency affects reliability 2

Clinical Applications

Trauma and Massive Transfusion

• Can guide component therapy based on specific deficiencies 2, 5
• Helps identify hyperfibrinolysis requiring antifibrinolytic therapy 2
• May predict need for massive transfusion, but not consistently superior to routine tests 1, 5

Liver Disease

• Often reveals rebalanced hemostasis despite abnormal conventional tests 2
• TEG-guided transfusion can reduce unnecessary blood product use in cirrhotic patients with nonvariceal bleeding 6

Obstetric Applications

• Can detect pregnancy-associated hypercoagulability 1, 2
• Monitors hemostatic changes in preeclampsia/eclampsia 1
• Can detect anticoagulant effects of heparin and LMWH 1, 2

Practical Interpretation Algorithm

1. Establish baseline

   • Compare results to institution-specific reference ranges 2
   • Consider patient factors (gender, pregnancy status) that affect normal values 1, 3

2. Identify pattern abnormalities

   • Hypercoagulable pattern: shortened R and K times, increased α-angle and MA 2
   • Hypocoagulable pattern: prolonged R and K times, decreased α-angle and MA
   • Hyperfibrinolysis: normal initial parameters with declining amplitude after MA 2

3. Correlate with clinical context

   • Interpret results alongside conventional coagulation tests 1
   • Consider limitations in specific clinical scenarios 1, 2

4. Guide interventions based on specific deficiencies

   • Prolonged R time: consider plasma or factor concentrates
   • Low MA with normal fibrinogen: consider platelet transfusion
   • Low MA with low fibrinogen: consider cryoprecipitate or fibrinogen concentrate
   • Evidence of hyperfibrinolysis: consider antifibrinolytics

Important Caveats

• TEG and ROTEM results are not interchangeable due to different reagents and hardware 1, 2
• Women tend to be more hypercoagulable than men on TEG parameters 3
• Local reference ranges should be established as they are device and manufacturer-specific 2, 3
• Specialized TEG tests (heparinase, functional fibrinogen) provide additional information in specific scenarios 2

TEG provides valuable information about global hemostasis but must be interpreted with an understanding of its limitations and in conjunction with clinical assessment and conventional coagulation tests.