Interpreting Thromboelastography (TEG) Parameters and Clinical Applications

Key TEG Parameters and Their Interpretation

The International Society on Thrombosis and Haemostasis recommends that R time (Reaction time) measures time to initial fibrin formation (clot initiation) 1
Prolonged R time suggests coagulation factor deficiency or anticoagulant effect, according to the International Society on Thrombosis and Haemostasis 2
Shortened R time indicates hypercoagulability, as stated by the International Society on Thrombosis and Haemostasis 2, 1
The International Society on Thrombosis and Haemostasis states that K time (Kinetics) is the time from clot initiation to reach 20mm clot width 2
Prolonged K time indicates delayed clot formation, according to the International Society on Thrombosis and Haemostasis 2
Shortened K time suggests increased rate of clot formation, as stated by the International Society on Thrombosis and Haemostasis 2, 3
Increased alpha angle indicates faster clot formation, according to the International Society on Thrombosis and Haemostasis 2
Decreased alpha angle suggests slower clot formation, as stated by the International Society on Thrombosis and Haemostasis 2, 3
The International Society on Thrombosis and Haemostasis recommends that Maximum Amplitude (MA) represents maximum strength of the clot 3
Decreased MA suggests thrombocytopenia or platelet dysfunction, according to the International Society on Thrombosis and Haemostasis 2
Increased MA indicates hypercoagulability, as stated by the International Society on Thrombosis and Haemostasis 2, 1

Fibrinolysis Parameters

The International Society on Thrombosis and Haemostasis states that LY30 is the percentage of clot lysis 30 minutes after MA is reached 4
Increased LY30 (>7.5%) indicates hyperfibrinolysis and predicts need for massive transfusion, according to the International Society on Thrombosis and Haemostasis 4
Decreased LY30 suggests impaired fibrinolysis, as stated by the International Society on Thrombosis and Haemostasis 4

Clinical Applications

The International Society on Thrombosis and Haemostasis recommends the use of TEG in obstetrics to reflect hypercoagulable state of pregnancy 5
TEG shows progressive resolution of hypercoagulability postpartum, according to the International Society on Thrombosis and Haemostasis 2, 1
The International Society on Thrombosis and Haemostasis states that TEG can detect coagulation changes during cesarean delivery 2

Limitations and Pitfalls

The International Society on Thrombosis and Haemostasis recommends that TEG cannot detect von Willebrand disease or disorders affecting endothelial adherence 6
Standard TEG is insensitive to antiplatelet agents and cannot reliably detect platelet dysfunction, according to the International Society on Thrombosis and Haemostasis 6
TEG shows high coefficients of variance (7.1-39.9% for TEG parameters), as stated by the International Society on Thrombosis and Haemostasis 7, 8
Results vary between devices and are not interchangeable between TEG and ROTEM, according to the International Society on Thrombosis and Haemostasis 7
Proper training and regular calibration are essential, as recommended by the International Society on Thrombosis and Haemostasis 7, 6
Anemia can paradoxically show hypercoagulable TEG results due to decreased blood viscosity, according to the International Society on Thrombosis and Haemostasis 6
TEG is performed at 37°C and cannot assess effects of hypothermia, as stated by the International Society on Thrombosis and Haemostasis 6

Best Practices for TEG Interpretation

The International Society on Thrombosis and Haemostasis recommends using device-specific reference ranges, as results vary between different TEG systems 7
Consider the clinical context when interpreting results, especially in pregnancy, trauma, or liver disease, as stated by the International Society on Thrombosis and Haemostasis 2
TEG provides a global assessment of hemostasis but has limitations in detecting specific coagulation disorders, according to the International Society on Thrombosis and Haemostasis 6
For fibrinolysis assessment, recognize that TEG may have limited sensitivity in detecting hypofibrinolysis, as stated by the International Society on Thrombosis and Haemostasis 4, 6

Correcting Prolonged R Time in Thromboelastography (TEG)

Introduction to Correction Strategies

To correct a prolonged R time in TEG, administer fresh frozen plasma (FFP) or prothrombin complex concentrate (PCC), with fibrinogen concentrate if needed, guided by the specific cause of the prolongation 9

For Vitamin K Antagonists (VKAs), the American College of Surgeons recommends administering PCC along with intravenous vitamin K for urgent correction, with dosing guided by INR level 10
For Dabigatran, TEG can be used to monitor the reversal effectiveness of idarucizumab (Praxbind) 11
For Factor Xa Inhibitors, the World Health Organization suggests administering andexanet alfa or PCC, and monitoring effectiveness with anti-Xa assays rather than TEG alone 11

Treatment of Coagulopathy

In cases of dilutional coagulopathy, the American College of Surgeons recommends administering FFP (10-15 mL/kg) as first-line treatment, and considering fibrinogen concentrate (4g/70kg) if significant hemodilution (>50%) is present 9
For massive transfusion scenarios, the American College of Surgeons recommends maintaining a 1:1:1 ratio of packed RBCs, FFP, and platelets 12

Monitoring and Special Considerations

Repeat TEG 15-30 minutes after intervention to assess response, with a target R time normalization (typically <8 minutes) 9
In pregnancy, baseline R times are typically shortened due to physiologic hypercoagulability, according to the American College of Obstetricians and Gynecologists 13
In liver disease, viscoelastic tests like TEG may guide more targeted blood product use with fewer transfusions, as suggested by the European Association for the Study of the Liver 14
In trauma patients, goal-directed therapy using TEG parameters has been shown to improve survival and reduce blood product waste compared to conventional coagulation test-guided therapy, according to the Trauma Committee of the American College of Surgeons 9

Correcting High Maximum Amplitude on Thromboelastography

Treatment Approach

For severe hypercoagulability or high thrombotic risk, consider therapeutic anticoagulation with low molecular weight heparin (LMWH) or unfractionated heparin (UFH), with LMWH preferred over UFH in pregnant patients due to better safety profile 15, 16
The International Society on Thrombosis and Haemostasis recommends considering therapeutic anticoagulation for severe hypercoagulability or high thrombotic risk, with LMWH or UFH as options, and LMWH preferred in pregnant patients 15, 16

Special Considerations

Pregnancy naturally induces a hypercoagulable state with increased MA values, which may not require correction unless extremely elevated, as suggested by the American College of Obstetricians and Gynecologists 16, 17
In liver disease, viscoelastic tests like TEG provide more valuable information than standard coagulation tests, but interpretation requires careful consideration of the clinical context, according to the American Association for the Study of Liver Diseases 18

Pitfalls to Avoid

Anemia can paradoxically show hypercoagulable TEG results due to decreased blood viscosity, potentially exaggerating the MA value, as noted by the American Society of Hematology 19
TEG shows high coefficients of variance (7.1-39.9% for TEG parameters), so results should be interpreted with caution and in clinical context, as recommended by the International Society on Thrombosis and Haemostasis 19
Results vary between devices and are not interchangeable between TEG and ROTEM systems, as stated by the International Society on Thrombosis and Haemostasis 19
TEG is performed at 37°C and cannot assess effects of hypothermia on coagulation, as noted by the American Society of Anesthesiologists 19

Correcting High Maximum Amplitude on Thromboelastography

Treatment Algorithm for High MA

The American College of Cardiology recommends LMWH over UFH in pregnant patients due to its better safety profile and more predictable anticoagulant effect, with 40mg enoxaparin showing greater anticoagulant effect than 7500 IU UFH, resulting in 73% of patients becoming hypocoagulable with LMWH versus only 47% with UFH 20, 21
The anticoagulant effect on TEG is defined as a difference >25% between plain and heparinase R time samples, with LMWH preferred due to its more predictable effect 20

Special Considerations

Pregnancy

Pregnancy naturally induces a hypercoagulable state with increased MA values, according to the American College of Obstetricians and Gynecologists 22
Women with mild preeclampsia are more hypercoagulable compared to healthy pregnant women, with a higher risk of thrombotic events 20
As preeclampsia severity worsens, blood coagulability decreases, particularly in women with low platelet counts, as reported by the National Institute of Child Health and Human Development 20

Obesity

Studies show a trend of increasing hypercoagulability with increasing body mass index (BMI), according to the American Heart Association 20

Maximum Amplitude in TEG Reflects Platelet Function

Understanding TEG Parameters and Platelet Function

Maximum Amplitude (MA) represents the maximum strength of the clot and primarily reflects platelet function and fibrinogen contribution, as noted by the International Society on Thrombosis and Haemostasis 23

Limitations of TEG in Assessing Platelet Function

Standard TEG is insensitive to antiplatelet agents and cannot reliably detect platelet dysfunction, according to the International Society on Thrombosis and Haemostasis 23, 24
TEG cannot assess the contribution of endothelium to coagulation, so it cannot detect von Willebrand disease or other conditions affecting endothelial adherence, as stated by the International Society on Thrombosis and Haemostasis 24

Advanced TEG Methods for Platelet Function Assessment

The contribution of platelets to clot strength can be quantified by comparing standard TEG with modified TEG using platelet inhibitors, as suggested by the International Society on Thrombosis and Haemostasis 23
Some studies suggest calculating platelet contribution by subtracting the maximum clot elasticity of FIBTEM from EXTEM in ROTEM systems, as reported by the International Society on Thrombosis and Haemostasis 24

Clinical Implications

Low MA values may indicate need for platelet transfusion, as recommended by the Society of Critical Care Medicine 25

Common Pitfalls in TEG Interpretation

TEG is performed at 37°C and cannot assess effects of hypothermia on coagulation, as noted by the International Society on Thrombosis and Haemostasis 24

Thromboelastography in Clinical Practice

Introduction to Thromboelastography

TEG is a point-of-care viscoelastic testing device that uses whole blood samples to assess the entire coagulation process in real-time, from initial clot formation through clot strength to fibrinolysis, providing a dynamic global assessment of hemostatic function at the patient's bedside 26

Clinical Applications

TEG has been studied extensively in cardiac surgery where data support its use to reduce morbidity associated with transfusion, allowing for directed blood component resuscitation among patients with acute blood loss and coagulopathy 26
TEG can detect the hypercoagulable changes associated with pregnancy, showing progressive increases in coagulability that correlate with pregnancy progression 26
ROTEM may be used to guide transfusion therapy for postpartum hemorrhage, though only two randomized controlled trials exist on TEG/ROTEM use in obstetrics as of 2020 26
The hypercoagulable state of pregnancy persists for at least the first 24 hours postdelivery as detected by TEG 27

Anticoagulation Monitoring

TEG can detect anticoagulant effects, defined as a difference >25% between plain and heparinase R time samples 28
The device has been used to monitor effects of unfractionated heparin, low molecular weight heparin, and direct oral anticoagulants, though sensitivity varies by agent 28

Evidence Quality and Research Gaps

Variability between study protocols and results suggests the need for future large prospective high-quality studies with standardized protocols to investigate utility of TEG/ROTEM in assessing risk for thrombosis and hemorrhage 26

Hypercoagulability Indicators on Thromboelastography

Understanding R Time and Hypercoagulability

R time measures the time from test initiation to initial fibrin formation, representing the clotting time or time to clot initiation, with values typically ranging, but the normal range is not cited here 29, 30

Clinical Significance of Low R Time

Pregnancy naturally shortens R time due to physiologic hypercoagulability, with progressive decreases correlating with pregnancy advancement 30, 31, 32
Post-cesarean delivery, R time becomes even shorter, indicating increased hypercoagulability that peaks at 3 hours postoperatively 30, 31
General anesthesia during cesarean delivery causes significantly decreased R time compared to spinal anesthesia, indicating faster clotting 29, 30

Pathophysiology and Clinical Implications

Enhanced thrombin generation can result in low R time, indicating accelerated initiation of the coagulation cascade 29
Evaluate for underlying hypercoagulable conditions, including pregnancy, malignancy, inflammatory states, or inherited thrombophilias, when low R time is observed 31, 32

Important Considerations for Interpretation and Management

Colloid preloading is associated with longer R times compared to crystalloid preloading, so fluid type affects results 29, 30

Effects of Anticoagulation and Test Correlation on Kaolin‑Activated TEG R‑Time

Anticoagulant Effects on R‑Time

Heparin therapy (both unfractionated and low‑molecular‑weight) prolongs the kaolin‑activated TEG R‑time by inhibiting thrombin generation, reflecting delayed clot initiation in patients receiving heparin. 33

Correlation with Conventional Coagulation Tests

In patients supported by extracorporeal membrane oxygenation (ECMO), the INTEM clotting time shows a moderate correlation with standard assays (aPTT R² = 0.34; ACT R² = 0.30), whereas the kaolin‑activated TEG R‑time does not correlate significantly with these conventional tests, indicating limited comparability in this setting. 34
Overall, TEG provides complementary but not interchangeable information compared with conventional coagulation tests, underscoring the need for combined interpretation when assessing hemostasis. 33

TEG R‑time Correlation with Direct Oral Anticoagulants and Monitoring of Reversal

Correlation of TEG R‑time with DOAC Levels

In patients receiving a direct thrombin inhibitor, the TEG R‑time correlates with the plasma concentration of the drug, providing a quantitative bedside measure of anticoagulant effect. 35
In patients receiving a factor Xa inhibitor, the TEG R‑time shows a moderate correlation with prothrombin time (PT), offering an additional point‑of‑care indicator of anticoagulation intensity. 35

TEG‑guided Reversal of Dabigatran

Following administration of the specific antidote idarucizumab, TEG can be used to monitor the normalization of coagulation parameters, confirming effective reversal of dabigatran‑induced anticoagulation. 35

Limitations of Thromboelastography in Identifying Specific Coagulation Deficiencies

Parameters Assessed by TEG

TEG evaluates the viscoelastic properties of whole‑blood clot formation using the following global parameters: Reaction time (R), Kinetics (K), Alpha angle, Maximum Amplitude (MA), and LY30 (percentage lysis at 30 min)【36】【37】.

Inability to Detect Specific Factor Deficiencies

Although a prolonged R time may indicate a coagulation factor deficiency or anticoagulant effect, TEG cannot differentiate which individual factor (e.g., factors II, V, VII, VIII, IX, X, XI, or XII) is deficient【38】.
Consequently, conventional laboratory tests such as PT/INR, aPTT, and specific factor assays remain necessary to pinpoint the exact deficiency【38】.

Failure to Identify Primary Hemostasis Disorders

TEG does not assess endothelial contributions to coagulation and therefore cannot detect von Willebrand disease or other disorders that rely on endothelial adhesion【39】.
Because TEG employs reagents that bypass primary hemostasis, it is insensitive to antiplatelet agents and cannot reliably identify platelet dysfunction【39】.

Limited Sensitivity for Fibrinolysis

In pregnancy, TEG shows limited ability to detect hypofibrinolysis, as fibrinolytic activity may be confined to the placenta and not reflected in systemic measurements【39】.
The normal reference range for ROTEM CLI30 (94 %–100 %) makes it impossible for TEG to distinguish normal from hyperfibrinolysis in this setting【39】.

Situations Where TEG Provides Useful Global Information

TEG can demonstrate a progressive increase in global hypercoagulability throughout gestation, correlating with advancing pregnancy weeks【36】【37】.
An LY30 value greater than 7.5 % identifies hyperfibrinolysis, which predicts the need for massive transfusion and is associated with higher mortality【40】.

Necessity for Complementary Laboratory Testing

When TEG abnormalities are observed, additional testing—including specific factor assays, PT/INR, aPTT, fibrinogen level, platelet count, and dedicated platelet‑function studies—is essential to define the precise hemostatic defect【38】【39】.
In patients with liver disease, viscoelastic testing adds valuable information beyond standard coagulation tests, but interpretation must be supplemented with traditional assays to guide management【38】.