What can TEG® analysis measure?
TEG® technology is consistent with recent advances in the understanding of hemostasis by analyzing the functional activities of the cellular elements, such as platelet cytoplasmic granules and platelet surfaces, in conjunction with plasma components. Because the TEG® analyzer monitors the shear elasticity of clotting blood, a physical property, the TEG® analyzer is sensitive to all the interacting cellular and plasmatic components such as coagulation and fibrinolytic factors, activators, and inhibitors, that may effect the rate or structure of a clotting sample and its breakdown.

The TEG® analyzer measures the mechanical properties of the developing clot:

• The time until initial fibrin formation.
• The kinetics of the initial fibrin clot to reach maximum strength.
• The ultimate strength and stability of the fibrin clot and therefore its ability to do the work of hemostasis -- to mechanically impede hemorrhage without permitting inappropriate thrombosis.

TEG® analyzer technology

The TEG® analyzer has a sample cup that oscillates back and forth constantly at a set speed through an arc of 4°45'. Each rotation lasts ten seconds. A whole blood sample of 360 ul is placed into the cup, and a stationary pin attached to a torsion wire is immersed into the blood. When the first fibrin forms, it begins to bind the cup and pin, causing the pin to oscillate in phase with the clot. The acceleration of the movement of the pin is a function of the kinetics of clot development.

The torque of the rotating cup is transmitted to the immersed pin only after fibrin-platelet bonding has linked the cup and pin together. The strength of these fibrin-platelet bonds affects the magnitude of the pin motion, such that strong clots move the pin directly in phase with the cup motion. Thus, the magnitude of the output is directly related to the strength of the formed clot. As the clot retracts or lyses, these bonds are broken and the transfer of cup motion is diminished. The rotation movement of the pin is converted by a mechanical-electrical transducer to an electrical signal which can be monitored by a computer.

The resulting hemostasis profile is a measure of the time it takes for the first fibrin strand to be formed, the kinetics of clot formation, the strength of the clot (in shear elasticity units of dyn/cm2) and dissolution of clot.

Clot dynamics
The resultant hemostasis profile can be evaluated and individual points in the profile indicate specific parameters of patient hemostasis:

Clotting time	R	The period of time of latency from the time that the blood was placed in the TEG® analyzer until the initial fibrin formation.
Clot kinetics	K	A measure of the speed to reach a specific level of clot strength.
	alpha	Measures the rapidity of fibrin build-up and cross-linking (clot strengthening)
Clot strength	MA,G	A direct function of the maximum dynamic properties of fibrin and platelet bonding via GPIIb/IIIa and represents the ultimate strength of the fibrin clot.
Hemostasis profile	CI	Coagulation Index, which is a linear combination of the above parameters.
Clot stability	LY30	Measures the rate of amplitude reduction 30 minutes after MA.

It is important to stress here that the standard coagulation tests - PT, PTT, TT, fibrinogen level, etc. - stop measuring at the first stage of coagulation, when the first clot is formed. They are plasma tests measuring plasma hemostasis and not patient hemostasis, which is in whole blood, and they ignore the important role of platelets and phospholipids in the role of coagulation.

Other parameters (shown in the figure above) measure other aspecs of hemostasis,such as time to maximum clot strength (TMA), and clot lysis time (CLT).

Modified Blood Samples

Native whole blood samples provide the most sensitive method for analysis. However, most times it is not practical or necessary to run a straight native sample.  For instance, samples can be citrated to prolong storage time. A wealth of additional information can be obtained by running blood samples that have been modified before application on the analyzer. For example:

• measure heparin effect using heparinase cups and pins
• speed analysis by adding kaolin or other activators
• test functional fibrinogen level by adding tissue factor and ReoPro
  
• test in vitro for the effect of any drug on a patient by adding it to the sample in a similar concentration
  
  

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