science

Thromboelastography

Thromboelastography is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Thromboelastography rather than just read about it. In short: Thromboelastography (TEG) is a method of testing the efficiency of blood coagulation. It is a test mainly used in surgery and anesthesiology, although increasingly used in resuscitations in emergency departments, intensive care units, and labor and delivery suites.

Key takeaways

Thromboelastography belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Thromboelastography to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Thromboelastography from memory before moving on to harder problems.

Reference excerpt

Thromboelastography (TEG) is a method of testing the efficiency of blood coagulation. It is a test mainly used in surgery and anesthesiology, although increasingly used in resuscitations in emergency departments, intensive care units, and labor and delivery suites. More common tests of blood coagulation include prothrombin time (PT) and partial thromboplastin time (aPTT) which measure coagulation factor function, but TEG also can assess platelet function, clot strength, and fibrinolysis which these other tests cannot. Thromboelastometry (TEM), previously named rotational thromboelastography (ROTEG) or rotational thromboelastometry (ROTEM), is another version of TEG in which it is the sensor shaft, rather than the cup, that rotates.

Mechanics

A small sample of blood is taken from the selected person and rotated gently through 4º 45', six times a minute, to imitate sluggish venous flow and activate coagulation. The clot forms around a thin wire probe used for measurement. The speed and strength of clot formation is measured in various ways, typically by computer. The speed at which the sample coagulates depends on the activity of the plasma coagulation system, platelet function, fibrinolysis and other factors which can be affected by genetics, illness, environment, and medications. The patterns of changes in strength and elasticity in the clot provide information about how well the blood can perform hemostasis and how well or poorly different factors are contributing to clot formation. Four values that represent clot formation are determined by this test: the reaction time (R value), the K value, the angle and the maximum amplitude (MA). The R value represents the time until the first evidence of a clot is detected. The K value is the time from the end of R until the clot reaches 20mm and this represents the speed of clot formation. The angle is the tangent of the curve made as the K is reached and offers similar information to K. The MA is a reflection of clot strength. A mathematical formula determined by the manufacturer can be used to determine a Coagulation Index (CI) (or overall assessment of coagulability) which takes into account the relative contribution of each of these 4 values into 1 equation. The G-value is a log-derivation of the MA and is meant to also represent the clot strength using dynes/sec as its units. There are some studies which suggest that an elevated G-value is associated with a hypercoagulable state and therefore increases the risk for venous thromboembolic disease. However, there are no studies dosing of prophylactic heparin products based on the G-value. TEG also measures clot lysis which is reported as both the estimated percent lysis (EPL) and the percentage of clot which has actually lysed after 30 minutes (LY 30,%). Although a normal EPL can be as high as 15% and a normal LY 30 can be as high as 8%, some studies in the trauma population suggest that a LY30 greater than 3% is associated with risk of hemorrhage. Thromboelastometry (TEM), previously named rotational thromboelastography (ROTEG) or rotational thromboelastometry (ROTEM), is another version of TEG in which it is the sensor shaft, rather than the cup, that rotates. Blood (300 μL, anticoagulated with citrate) is placed into the disposable cuvette using an electronic pipette. A disposable pin is attached to a shaft which is connected with a thin spring (the equivalent to Hartert's torsion wire in thrombelastography) and slowly oscillates back and forth. The signal of the pin suspended in the blood sample is transmitted via an optical detector system. The test is started by adding appropriate reagents. The instrument measures and graphically displays the changes in elasticity at all stages of the developing and resolving clot. The typical test temperature is 37 °C, but different temperatures can be selected, e.g. for patients with hypothermia.

Parameters

Parameters derived from thromboelastography are mainly:

R time: Time to initial clot formation (that is, amplitude deviation from baseline) K time: Time from initial clot formation until reaching 20 mm in amplitude Alpha angle (α): Angle between the baseline at initial clot formation, and a tangent line that intersects the tracing curve. Maximum amplitude (MA): Maximum deviation of tracing to baseline. A30: Amplitude 30 minutes after reaching maximum amplitude.

Interpretation Following are examples of thromboelastography patterns and recommended treatments.

Assay types

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Thromboelastography

Start with the simplest possible case. Write down what Thromboelastography claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Thromboelastography before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Thromboelastography ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Thromboelastography

In research: Thromboelastography appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Thromboelastography in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Thromboelastography is common in secondary-school and first-year university syllabi. It links to neighbouring topics Blood tests, Coagulation system, so understanding it makes those chapters shorter.
In everyday life: Look for Thromboelastography outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Thromboelastography in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Thromboelastography means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Thromboelastography out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Thromboelastography in simple terms?

Why does Thromboelastography matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Thromboelastography?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Thromboelastography.