A Practical Guide to Haemostasis

Thromboelastography [TEG] &
Rotational Thromboelastometry [ROTEM]


Thromboelastography [TE] was first described by Hartert in 1948. Thromboelastography (TEG) and Thromboelastometry (ROTEM) provide global information on the dynamics of clot development, stabilisation and dissolution that reflect in vivo haemostasis. Although TE has not been subjected to the same evaluation processes as conventional haemostatic tests, its use as a POCT monitor in complex major surgery has been shown to significantly reduce the use of blood component therapy and overall blood loss. Thromboelastography is commonly used in the trauma setting - see References for additional information.

The TEG and ROTEM are increasingly used in pregnancy and the puerperium.  Pregnancy is a hypercoagulable state and this is reflected in the TEG and ROTEM parameters.  It may not, therefore, be appropriate to use reference ranges for the TEG and ROTEM that have been derived from non-pregnant individuals. For further information and for reference ranges that have been derived in pregnancy - see References.

For additional information on viscoelastic elastic assays and emerging technologies - see Hartman et al 2020.


The figures below shows the traces obtained using the TEG and ROTEM whilst the table summarises the descriptive data reported with both the TEG and ROTEM.

1. Thromboelastogram [TEG®]


2. TEG6s Analyzer

The TEG6s analyser uses resonance-frequency viscoelastic measurement and a disposable all-in-one cartridge.  The blood sample is suspended in a multi-channel cartridge and then exposed to external vibration (20–500 Hz). As clotting proceeds and the blood sample changes state, the elasticity and resonant frequency increase.  These changes in the clot-strength-specific resonance frequencies are detected by a photo-detector and converted into TEG-equivalent units.  These are used to generate TEG tracings and which outline the viscoelastic change of the blood sample in real time. 

A number of cartridges are available and which allow various aspects of haemostasis to be analysed in real-time.  For further information - see Link to Haemonetics and TEG6s.



Variables measured by the TEG® and ROTEM®

Variable TEG® ROTEM®
Measurement period - Reaction Time [RT]
Time from start to when the waveform reaches 2mm above baseline R Clotting Time [CT]
The time from 2mm above baseline to 20mm above baseline K Clot Formation Time [CFT]
Alpha angle [°] Slope between R and K Angle of tangent at 2mm amplitude
Maximum angle - CRF
Maximum strength Maximal Amplitude [MA] Maximal Clot Firmness [MCF]
Time to Maximum strength - MCF-t
Amplitude at a specific time A30, A60 A5, A10...
Clot elasticity G MCE
Maximum lysis - CLF
Clot Lysis [CL] at a specific time [minutes] CL30, CL60 LY30, LY45, LY60
Time to lysis 2mm from MA CLT [10% difference from MCF]


Whole blood is added to a heated cuvette at 37°C. Within the cup a pin is suspended connected to a detector system - this is a torsion wire in the case of TEG and an optical detector in the case of the ROTEM device. The cup and pin move relative to each other through an angle of 4°45'. The movement is initiated from either the cup (TEG) or the pin (ROTEM). As the blood clots, fibrin strands form between the cup and pin and rotation of the cup is transmitted to pin in the case of the TEG or impedes rotation of the pin in the case of the ROTEM. This is detected and a trace generated - see above.

Although originally the TEG involved fresh whole non-anticoagulated blood, both the TEG and the ROTEM commonly employ citrated whole blood that is re-calcified to initiate coagulation. It is also common to use an activator as this standardises the test and in addition speeds up the rate at which clotting takes place and hence the rate at which a result is generated. The TEG and ROTEM devices have a number of separate channels allowing a number of samples to be run simultaneously or sequentially.

Modifications of the TEG and ROTEM Devices

Modification Interpretation
Tissue Factor The use of an activator when undertaking thromboelastography is generally recommended to standardise the initiation of the clotting process.
Tissue Factor activation of the TEG enables the maximal amplitude (MA) to be established within 10 minutes but will result in significant shortening of the reaction time (R value) and as a result much of this latter information is lost.
R Time and Heparinase The R value in a native TEG is sensitive to trace amounts of Heparin and endogenously released Heparan sulphate.
The use of a Heparinase-coated reaction cuvette for the TEG will demonstrate any Heparin present in the sample or in the patient and enables assessment of haemostasis in patients who are fully anticoagulated with Heparin e.g. on cardio-pulmonary bypass [CPB].
Tissue Factor/Kaolin activated TEG and the ACT By incorporating both Tissue Factor and Kaolin into the TEG cuvette, the TEG approximates to the Activated Clotting Time [ACT.]
Fibrinogen and Platelet function The MA is primarily a reflection of clot strength and is affected by changes in Fibrinogen, the platelet count and platelet function. The MA is established either from a native sample with no activator or from the combined Tissue Factor/Kaolin activated TEG. There is a strong linear correlation between the log platelet count and MA.

Abciximab is a potent platelet GpIIb/IIIa inhibitor and an Abciximab-modified TEG can help to discriminate between Hypofibrinogenaemia and Platelet dysfunction as a cause of a decreased MA.
Fibrinolysis The degree of fibrinolysis can be established from either a native sample with no activator, from the Tissue Factor activator or the combined Tissue Factor/Kaolin activated TEG.
Hyperfibrinolysis is increasingly recognised as a cause of peri-operative microvascular bleeding and is readily detected by analysing the clot lysis index on the TEG or ROTEM.
The ability to detect and determine the severity of fibrinolysis avoids empirical or inappropriate anti-fibrinolytic therapy.
Mathematical derivations of changes in elastic modulus derived from the amplitude have been used to quantify the extent of fibrinolysis in clinical and laboratory settings, as well as to guide antifibrinolytic therapy.
Hypercoagulability The TEG may be helpful in screening for hypercoagulable states. TEG analysis of patients with a history of thromboembolic complications showed shorter R values and accelerated clot propagation compared to healthy reference subjects.
PlateletMapping TEG The TEG PlateletMapping® assay provides a method for testing the ability of platelets to participate in clot formation with and without the contribution of anti-platelet drugs.

The assay involves four separate analyses on whole blood:
1. A Kaolin-activated TEG which generates Thrombin to activate platelets and cleave Fibrinogen.  This provides a measurement of overall clot strength.
2. A TEG in which heparin is used to inactivate Thrombin and Reptilase and Factor XIII are used generate a fibrin clot and to isolate the fibrin contribution to overall clot strength.
3. An ADP TEG in which platelets are activated using ADP.  This TEG includes Reptilase and Factor XIII.
4. An Arachidonic Acid TEG which activate the platelets via the TxA2 pathway. This TEG includes Reptilase and Factor XIII.

By comparing the relative clot strengths of the 4 assays, it is possible to determine the degree of platelet inhibition in the presence of defined anti-platelet agents.


Rotational Thromboelastometry (ROTEM®)

The ROTEM analyser provides a trace similar to that of the TEG with related parameters including clotting time (CT) and maximum clot firmness (MCF). Additional tests include:

Test Interpretation
INTEM Contains Phospholipid and Ellagic acid as activators and provides information similar to that of the APTT
EXTEM Contains Tissue Factor as an activator and provides information similar to that of the PT
HEPTEM Contains lyophilised Heparinase for neutralising heparin.
Coagulation is initiated as for the INTEM.
APTEM Contains Aprotinin for inhibiting fibrinolysis.
Coagulation is initiated as in the EXTEM. A comparison of the data from the EXTEM and the APTEM allows for the rapid detection of hyperfibrinolysis and in addition can determine if antifibrinolytic therapy alone will normalise coagulation or if additional treatments such as Fibrinogen supplementation, is necessary.
FIBTEM Based upon the INTEM but in addition contains Cytochalasin D, a platelet inhibitor which blocks the platelet contribution to clot formation, allowing a qualitative analysis of the functional Fibrinogen component.
ECATEM Contains Ecarin and so is similar to the Ecarin Clotting Time. This makes it very sensitive to presence of Direct Thrombin Inhibitors [DTIs].

First Derivative:
The rate and amount of Thrombin generation is considered to be predictive of the risk of thrombosis or haemorrhage. The TEG system provides the 'Thrombus Generation Velocity Curve' [see References] - the first derivative of the standard TEG waveform. Although the graph appears similar to that of a Thrombin Generation Test, it provides different information. In addition to providing information on thrombus generation it can provide similar information on the rate of thrombus lysis.
Similar curves can be generated using the ROTEM device.


See references for further information on the interpretation of the various traces generated by the TEG and ROTEM.

Reference Ranges

It is important to remember that the shape of the waveform is often as useful as the results of individual values. Reference ranges will also change depending upon whether a test uses an activator [e.g. Tissue Factor or not i.e. a native blood sample], the age of the patient and in the case of a female, if pregnant.

EQA Schemes

Internal Quality Control [IQC] and External Quality Assurance [EQA] are a fundamental part of any test that a laboratory offers and this includes viscoelastic haemostatic assays. NEQAS BC in the UK provides an EQA scheme for viscoelastic haemostatic assays - see LINKS.

Emerging Technologies

A number of novel methods for point-of-care visocelastic haemostatic assays in develpment and these include:
- Laser Speckle Rheometry
- Mechanical Resonant Frequency
- Ultrasonic Deformation
- Parallel Plate Viscometry
- Traditional Viscoelastic Testing with 'Active Tips'

...for more information - see Hartmann et al 2020.

What Test Next

On the basis of the TE traces, additional tests may be suggested. However, the TEG and ROTEM machines are often used to both investigate disorders of haemostasis and guide blood product replacement without any additional tests and they may, therefore, be performed in isolation.