Thromboelastogram (TEG)

Reviewed and revised 11 July 2014

OVERVIEW

  • Thromboelastography is a viscoelastic hemostatic assay that measures the global visco-elastic properties of whole blood clot formation under low shear stress
  • it shows the interaction of platelets with the coagulation cascade (aggregation, clot strengthening, fibrin cross linking and fibrinolysis)
  • does not necessarily correlate with blood tests such as INR, APTT and platelet count (which are often poorer predictors of bleeding and thrombosis)
  • This page describes TEG® predominantly, ROTEM® is the alternative viscoelastic hemostatic assay that is widely available

METHOD

  • TEG® measures the physical properties of the clot in whole blood via a pin suspended in a cup (heated to 37C)  from a torsion wire connected with a mechanical–electrical transducer
  • The elasticity and strength of the developing clot changes the rotation of the pin, which is converted into electrical signals that a computer uses to create graphical and numerical output
  • point of care test (quick, takes around 30min)
  • can be repeated easily and compared and contrasted
  • requires calibration 2-3 times daily
  • should be performed by trained personnel
  • susceptible to technical variations
  • kaolin and more recently kaolin + tissue factor (TF) (RapidTEG®) are used as activators, NATEM (TEG® using native whole blood is slower)
  • other tests are available including functional fibrinogen, a measure of fibrin-based clot function, and Multiplate which evaluates platelet function

TEG 1

USE

Indications

  • prediction of need for transfusion (MA is a useful predictor in trauma)
  • guide transfusion strategy

Studies show cost-effectiveness and reduction in blood products in:

  • liver transplantation
  • cardiac surgery

May be useful in:

  • trauma (reduction in blood product use and mortality in cohort studies)
  • obstetrics (some data to show that it may decrease transfusion rates; this is controversial)
  • early detection of dilutional coagulopathy

Hard to interpret in certain situations:

  • LMWH
  • aspirin
  • post cardiac bypass
  • fibrinolysis
  • hypercoagulability

NORMAL TEG

TEG 2

Specific parameters represent the 3 phases of the cell-based model of haemostasis: initiation, amplification, and propagation

  • R value = reaction time (s); time of latency from start of test to initial fibrin formation (amplitude of 2mm); i.e. initiation
  • K = kinetics (s); time taken to achieve a certain level of clot strength (amplitude of 20mm); i.e. amplification
  • alpha = angle (slope between R and K); measures the speed at which fibrin build up and cross linking takes place, hence assesses the rate of clot formation; i.e. thrombin burst
  • TMA = time to maximum amplitude(s)
  • MA = maximum amplitude (mm); represents the ultimate strength of the fibrin clot; i.e. overall stability of the clot
  • A30 or LY30 = amplitude at 30 minutes; percentage decrease in amplitude at 30 minutes post-MA and gives measure of degree of fibrinolysis
  • CLT = clot lysis time (s)

IMPORTANT PATTERNS

TEG 3

TEG AS A GUIDE TO TREATMENT

  • Increased R time => FFP
  • Decreased angle => cryopreciptate
  • Decreased MA => platelets (consider DDAVP)
  • Fibrinolysis =>  transexamic acid (or aprotinin or aminocaproic acid)

TEG® VERSUS ROTEM®

Comparison

  • Two commercial types of viscoelastic tests are available: thromboelastography =TEG® (developed in 1948, now produced  in the USA) and rotational thromboelastogram = ROTEM® (from Germany)
  • differences in diagnostic nomenclature for identical parameters between the two
  • TEG® operates by moving a cup in a limited arc (±4°45′ every 5s) filled with sample that engages a pin/wire transduction system as clot formation occur
  • ROTEM® has an immobile cup wherein the pin/wire transduction system slowly oscillates (±4°45′every 6s)
  • results are not directly comparable as different coagulation activators are used
  • ROTEM® is more resistant to mechanical shock, which may be an advantage in the clinical setting

Equivalent variables for ROTEM®

  • Clotting time (CT) = R value (reaction time)
  • α angle and clot formation time (CFT) = K value and α angle
  • Maximum clot firmness (MCF)  = Maximum amplitude (MA)
  • Clot lysis (CL)  = LY30

COMPARISON WITH PLASMA CLOTTING TESTS

Pros of viscoelastic hemostatic assays

  • assessment of global haemostatic potential provides more information than time to fibrin formation
  • can readily differentiate a coagulopathy due to low fibrinogen from one due to thrombocytopenia
  • point-of-care (POC) device with rapid  turnaround times so that many results available within 5–10 min of starting the test

Cons of viscoelastic hemostatic assays

  • variable availability
  • marked inter-operator variability and poor precision (UK NEQAS data suggests coefficients of variance ranging from 7.1% to 39.9% for TEG® and 7.0% to 83.6% for ROTEM®)
  • may require specialist staff to perform

VIDEO

Explanatory video by Joe Elbeery (consider muting the music):

References and Links

Journal articles

  • Afshari A, Wikkelsø A, Brok J, Møller AM, Wetterslev J. Thrombelastography (TEG) or thromboelastometry (ROTEM) to monitor haemotherapy versus usual care in patients with massive transfusion. Cochrane Database Syst Rev. 2011 Mar 16;(3):CD007871. doi: 10.1002/14651858.CD007871.pub2. Review. PubMed PMID: 21412912. [Free Full Text]
  • Bolliger D, Seeberger MD, Tanaka KA. Principles and practice of thromboelastography in clinical coagulation management and transfusion practice. Transfus Med Rev. 2012 Jan;26(1):1-13. doi: 10.1016/j.tmrv.2011.07.005. Epub 2011 Aug 26. Review. PubMed PMID: 21872428. [Free Fulltext]
  • da Luz LT, Nascimento B, Rizoli S. Thrombelastography (TEG(R)): practical considerations on its clinical use in trauma resuscitation. Scand J Trauma Resusc Emerg Med. 2013 Apr 16;21(1):29. [Epub ahead of print] PubMed PMID: 23587157. [Free Fulltext]
  • Ganter MT, Hofer CK. Coagulation monitoring: current techniques and clinical use of viscoelastic point-of-care coagulation devices. Anesth Analg. 2008 May;106(5):1366-75. doi: 10.1213/ane.0b013e318168b367. Review. PubMed PMID: 18420846. [Free Fulltext]

FOAM and web resources

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