What is TEG (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. 1
Core Technology and Mechanism
TEG measures viscoelastic properties of blood clotting by recording continuous changes in clot strength as fibrin polymerizes, providing a comprehensive picture of coagulation that standard tests cannot capture 2
The device works by measuring changes in viscoelastic strength of a small blood sample in response to constant rotational force, allowing visualization and quantification of blood coagulation including propagation, stabilization, and dissolution phases under low shear conditions 3
TEG is performed at 37°C at the patient's bedside, making it a rapid point-of-care technology with results available in approximately 30 minutes 4, 5
Key Parameters Measured
Clot Initiation Phase
R time (Reaction time) measures time to initial fibrin formation, with prolonged R time suggesting coagulation factor deficiency or anticoagulant effect, while shortened R time indicates hypercoagulability 4
K time (Kinetics) represents the time from clot initiation to reach 20mm clot width, with prolonged K indicating delayed clot formation and shortened K suggesting increased rate of clot formation 4
Alpha angle reflects the speed of clot formation, with increased angle indicating faster clot formation and decreased angle suggesting slower formation 4
Clot Strength Phase
Maximum Amplitude (MA) represents the maximum strength of the clot and primarily reflects platelet function and fibrinogen concentration, with decreased MA suggesting thrombocytopenia, platelet dysfunction, or fibrinogen deficiency 6, 4
Normal MA values typically range from 50-70 mm, with values <50 mm indicating significant clot strength impairment 6
Fibrinolysis Phase
- LY30 is the percentage of clot lysis 30 minutes after MA is reached, with increased LY30 (>7.5%) indicating hyperfibrinolysis and predicting need for massive transfusion 4
Clinical Applications
Surgical Settings
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 1, 7
The technology is used in liver transplantation, trauma, and major surgeries to optimize and minimize blood component usage by identifying specific coagulation defects 5, 3
Obstetric Applications
TEG can detect the hypercoagulable changes associated with pregnancy, showing progressive increases in coagulability that correlate with pregnancy progression 1, 4
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 1
The hypercoagulable state of pregnancy persists for at least the first 24 hours postdelivery as detected by TEG 1
Anticoagulation Monitoring
TEG can detect anticoagulant effects, defined as a difference >25% between plain and heparinase R time samples 1
The device has been used to monitor effects of unfractionated heparin, low molecular weight heparin, and direct oral anticoagulants, though sensitivity varies by agent 1, 4
Vascular Surgery
In cerebrovascular disease, TEG may predict presence and stability of carotid plaques, analyze platelet function before carotid stenting, and compare efficacy of antiplatelet therapy after stent deployment 7
For venous disease, TEG may predict hypercoagulability and thromboembolic events among various patient populations 7
Critical Limitations and Pitfalls
Technical Limitations
TEG shows high coefficients of variance (7.1-39.9% for TEG parameters), requiring proper training and regular calibration 6, 4
Results vary between devices and are not interchangeable between TEG and ROTEM systems, necessitating use of device-specific reference ranges 4
TEG is performed at 37°C and cannot assess effects of hypothermia on coagulation, a critical limitation in trauma settings 4
Diagnostic Blind Spots
Standard TEG is insensitive to antiplatelet agents and cannot reliably detect platelet dysfunction, limiting its utility in patients on antiplatelet therapy 6, 4
TEG cannot detect von Willebrand disease or disorders affecting endothelial adherence because it cannot assess the contribution of endothelium to coagulation 4
Anemia can paradoxically show hypercoagulable TEG results due to decreased blood viscosity, potentially masking coagulopathy 6, 4
Clinical Context Requirements
Do not rely solely on conventional coagulation tests (PT, aPTT) as they may not correlate well with TEG parameters, requiring integration of both testing modalities 6, 8
In pregnancy, baseline R times are typically shortened due to physiologic hypercoagulability, requiring pregnancy-specific reference ranges for interpretation 4
TEG provides a global assessment of hemostasis but has limitations in detecting specific coagulation disorders, necessitating additional hemostatic tests when applicable 2
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 1
While goal-directed therapy using TEG parameters has been shown to improve outcomes compared to conventional coagulation test-guided therapy in trauma patients, robust evidence in obstetrics remains limited 6
The technology has evolved from its inception in 1948 by Hartert, with modern methods providing more rapid and detailed kinetic data on fibrin generation, clot strength, and fibrinolysis 3