Thromboelastogram (TEG)

Reviewed and revised by Hamish Lala and Chris Nickson

OVERVIEW

Thromboelastography (TEG) is a viscoelastic hemostatic assay that measures the global viscoelastic properties of whole blood clot formation under low shear stress

• TEG 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 commercially

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

TEG6s (Haemonetics)

• This newer machine no longer uses the ‘pin-in-cup’ technique (as did its TEG5000 predecessor)
• It uses ‘resonance’ where blood is exposed to a fixed vibration frequency range and the detector measures the vertical motion of blood meniscus under LED illumination and transforms that movement into tracing of clot dynamics
• With pre-prepared cartridges, there is no longer any pipetting required!

USE

Indications

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

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

• liver transplantation
• cardiac surgery

Maybe 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:

• low molecular weight heparin (LMWH)
• aspirin
• post cardiac bypass
• fibrinolysis
• hypercoagulability

NORMAL TEG

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)
  • initiation phase
  • dependent on clotting factors
• K = kinetics (s)
  • time taken to achieve a certain level of clot strength (amplitude of 20mm)
  • amplification phase
  • dependent on fibrinogen
• alpha = angle (slope of line between R and K)
  • measures the speed at which fibrin build up and cross-linking takes place, hence assesses the rate of clot formation
  • “thrombin burst” / propagation phase
  • dependent on fibrinogen
• 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
  • dependent on platelets (80%) and fibrin (20%) interacting via GPIIb/IIIa
• A30 or LY30 = amplitude at 30 minutes
  • percentage decrease in amplitude at 30 minutes post-MA
  • fibrinolysis phase
• CLT = clot lysis time (s)

Approximate normal values (kaolin activated TEG, values differ if native blood used, and between types of assay)

• R: 4-8 min
• K: 1-4 min
• α-Angle: 47-74°
• MA: 55-73mm
• LY 30%: 0-8%

Corresponding terminology for ROTEM

ROTEM	TEG
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

IMPORTANT PATTERNS

TEG AS A GUIDE TO TREATMENT

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

Or use this handy guide (-:

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 and user familiarity
• 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

EVIDENCE

• Cochrane review (2015)of the use of TEG and ROTEM in traumatic bleeding advised that they should be used for research only, due to a lack of evidence for the accuracy of the assays.

References and Links

CCC Transfusion Series
Blood Products	Cryoprecipitate, Fresh Frozen Plasma (FFP), Platelets, Red Cells (RBCs) Concentrates: Prothrombinex, Factor VIIa, Fibrinogen Concentrate
Reversal	Rivaroxaban / Apixaban / Enoxaparin: Andexanet Alfa, Rivaroxaban and Bleeding Dabigatran: Idarucuzimab, Dabigatran and bleeding Heparin: Protamine Warfarin: Vitamin K / FFP / PTx, Warfarin Reversal, Warfarin Toxicity
Testing	Coagulation Studies, TEG / ROTEM (Thromboelastography), Platelet function assays
General Topics	Acute Coagulopathy of Trauma, Blood Bank, Blood conservation strategies, Blood Product Compatibilities, Blood transfusion risks, Disseminated Intravascular Coagulation, Massive blood loss, Massive transfusion protocol (MTP), Modifications to blood components,Procedures and Coagulopathy, Storage Lesions, TRALI, Transfusion Literature Summaries, Transfusion Reactions

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
• 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
• 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.
• 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
• Hunt H, Stanworth S, Curry N, Woolley T, Cooper C, Ukoumunne O, Zhelev Z, Hyde C. TEG and ROTEM for diagnosing trauma‑induced coagulopathy (disorder of the clotting system) in adult trauma patients with bleeding. Cochcane Review. 2015
• Tapia NM et al. TEG-guided resuscitation is superior to standardized MTP resuscitation in massively transfused penetrating trauma patients. J Trauma Acute Care Surg. 2013;74:378-386.
• Thakur M, Ahmed AB. A review of thromboelastography. Int J Periop Ultrasound Appl Technol 2012;1(1):25-29.
• Whiting D, DiNardo JA. TEG and ROTEM: technology and clinical applications. Am J Hematol. 2014 Feb;89(2):228-32. doi: 10.1002/ajh.23599. PMID: 24123050. [article]

FOAM and web resources

• ICN — SMACC: Hurn on TEG/ROTEM in the Real World (2013)
• Joe Elbeery on Youtube — TEG basics video (2013)
• Maryland CCP — The Use of TEG & Goal Directed Blood Component Therapy by John Walsh (2013)
• Practical-Hemostasis.com — TEG and ROTEM
• The websites for the ROTEM and TEG provide a comprehensive explanation of the waveforms generated in various disorders.

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