VCP 2010 Application of TEG/TEM to veterinary - UC Davis School ...

INVITED REVIEW 

Application of thrombelastography/thromboelastometry to 

veterinary medicine 

Amir Kol 1 , Dori L. Borjesson 2 

1 Veterinary Medical Teaching Hospital and 2 Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, 

University of California–Davis, Davis, CA, USA 

Key Words 

Coagulation, hemostasis, hypercoagulability, 

hypocoagulability, TEG 

Correspondence 

Dr. Amir Kol, Veterinary Medical Teaching 

Hospital, School of Veterinary Medicine, 

University of California–Davis, One Shields 

Avenue, Davis, CA 95616, USA 

E-mail: akol@ucdavis.edu 

DOI:10.1111/j.1939-165X.2010.00263.x 

I. Introduction 

II. Blood Samples and Instrumentation 

III. Terminology 

IV. TEG Variables and Correlation with Routine Coagulation Assays 

V. Validation Studies and Preanalytical Factors 

VI. Clinical Applications in Veterinary Medicine 

A. Hypercoagulable states 

B. Hypocoagulable states 

C. Monitoring anticoagulant therapy 

D. Platelet function 

VII. Summary 

Introduction 

Hemostasis is a complex physiologic process in which 

blood vessels, blood cells, and soluble factors in plasma 

interact in order to prevent hemorrhage and thrombosis. 

In 1856, the physician Rudolf Virchow suggested 

that altered blood flow, endothelial injury, and hypercoagulability 

contribute to the development of 

venous thrombosis (VT). These factors are known as 

Virchow’s triad and are still considered the basic 

Veterinary Clinical Pathology ISSN 0275-6382 

Abstract: Thrombelastograph analyzers are point-of-care hemostatic 

analyzers that provide global assessment of the hemostatic process. Thrombelastography 

(TEG) detects and provides a continuous recording of the 

changes in the viscoelastic properties of whole blood from initial clot 

formation through fibinolysis. TEG has been validated for use in dogs, horses, 

and cats. Hemostasis research using TEG has focused on test validation, alterations 

of TEG tracings in animals with naturally occurring diseases, and the 

use of TEG for monitoring various therapeutic modalities. This article reviews 

TEG methodology and terminology, including potential sources of preanalytical 

and analytical errors, the correlation between TEG and other routine 

hemostatic assays, and current clinical applications of TEG, with emphasis on 

veterinary medical practice. Data suggest that TEG may be a sensitive and 

useful adjunctive tool for evaluating an animal with an underlying coagulopathy, 

including hypercoagulability and hypocoagulability. Additional 

prospective studies are needed to (1) correlate TEG tracing patterns with a 

clinical predisposition for bleeding or thrombosis in various disease states and 

(2) determine whether monitoring and treating hemostatic disorders based 

on TEG tracings improve clinical outcome. 

underlying mechanisms of thrombosis today. 

Thrombelastography (TEG) is an in vitro diagnostic 

technique initially introduced in Germany in the late 

1940s by Hartert. 1,2 TEG integrates the cellular and 

soluble components of the hemostatic process to yield 

a global assessment of hemostasis. The technique is 

based on a continuous detection and recording of 

changes in the viscoelastic properties of whole blood 

while it clots. TEG tracings may better reflect the cellbased 

model of hemostasis 3 and thus better predict the 

kinetics of coagulation compared with routine plasmabased 

assays. Routine coagulation assays are limited in 

their capacity to predict hemorrhage or thrombosis, 

especially in patients who undergo invasive diagnostic 

and therapeutic procedures. The increased use and interest 

in TEG in veterinary medicine is based on the 

potential for TEG results to better predict thrombotic as 

well as hemorrhagic events in the clinical setting. 4,5 

The terms thrombelastography, thrombelastograph, 

and TEG were used generically in the scientific 

literature until 1996. At that time, Haemoscope Corporation 

(Niles, IL, USA) named its thrombelastograph 

Vet Clin Pathol 39/4 (2010) 405–416 c 2010 American Society for Veterinary Clinical Pathology 405

Application of TEG to veterinary medicine 

analyzer ‘‘TEG,’’ which became a registered trademark 

of the company. Later, a second analyzer, rotational 

thromboelastometry (ROTEM), became available (Pentapharm 

GmbH, Munich, Germany). The ROTEM analyzer 

is currently used primarily in Europe and has 

recently been approved by the US Food and Drug Administration 

for clinical use in the United States. 6 Comparison 

of TEG and ROTEM analyzers is beyond the 

scope of this review and for a more in-depth comparison 

the reader is referred elsewhere. 7,8 For the purpose 

of this article, ‘‘TEG’’ will be used generically, and the 

terms ‘‘Haemoscope TEG’’ or ‘‘ROTEM’’ will be used 

when referring to specific analyzers. 

TEG was originally designed to be a bed-side pointof-care 

analyzer that utilized whole nonanticoagulated 

blood. However, recent advances, including the use of 

anticoagulated blood and a variety of coagulation activators 

and specific inhibitors, have allowed TEG instrumentation 

to be utilized by diagnostic laboratories as 

well. 8 Since the 1980s, TEG has been widely used in clinical 

settings in human medicine, especially during liver 

transplantation and cardiac surgery. TEG results guide 

administration of blood products and anticoagulants and 

predict hemorrhage during surgery and postoperatively. 

9,10 In veterinary medicine, TEG and ROTEM have 

been validated for use in dogs, horses, and cats. 11–17 

The objectives of this review are to introduce TEG 

technique, including its strengths and limitations, 

highlight important preanalytical factors and quality 

control checkpoints that affect TEG results, review 

published data regarding clinical applications of TEG 

in human and veterinary medicine, and discuss potential 

future applications of this technique. 

Blood Samples and Instrumentation 

Blood should be collected atraumatically into sodium citrate 

(3.2% or 3.8%) anticoagulant. TEG protocols using 

anticoagulated citrated blood to which various activators 

are added have been validated for animals. The use of 

whole nonanticoagulated blood or anticoagulated blood 

without activation (recalcified method) is impractical in 

the veterinary setting and likely leads to an unacceptably 

high degree of intraassay variation. 12,13,17 Various 

activators and specific inhibitors are currently in use for 

TEG analysis. Standard reagents and products manufactured 

by Haemoscope Corporation for use with this 

company’s instrument are kaolin reagent, heparinasecoated 

cups for monitoring heparin therapy, and a rapid 

TEG (r-TEG) reagent that includes a mixture of kaolin 

and tissue factor (TF). Additional nonstandardized activators, 

including celite and recombinant human TF 

Figure 1. Haemoscope TEG analyzer with illustration of the composition 

of the cup, pin, and torsion wire and their oscillation pattern. Blood in a 

volume of 360 mL is placed in a cup preheated to 371C. The activator and 

calcium are added; then the pin is immediately introduced into the blood 

and oscillation begins. As a clot forms, the pin is engaged, represented 

by the ‘‘split point.’’ From this point on, 2 symmetrical branches are plotted 

(see Figure 2). Additional increases to the strength of the clot are indicated 

by increases in the tracing amplitude (graphic of the Haemoscope 

TEG thrombelastograph components [cup, pin, and wire] is reprinted with 

permission of Haemonetics Corporation, Braintree, MA, USA). 

(rhTF), are also in use. 17–20 Reagents for the ROTEM include 

a TF activator, a contact activator, a reagent that 

includes TF and a platelet inhibitor for qualitative assessment 

of fibrinogen, a TF and aprotonin mixture for 

detection of increased fibrinolysis, and a contact activator 

with heparinase for monitoring heparin therapy. 21 

Recalcification serves as the set point from which coagulation 

is initiated and the tracing begins. 

The TEG instruments consist of a pin attached to a 

torsion wire that is introduced into a cup, preheated to 

371C, containing a 360 mL aliquot of the blood sample 

(Figure 1). Movement is initiated by the cup (Haemoscope 

TEG) or the pin (ROTEM). As the blood 

clots, tension exerted on the wire is translated to an 

electrical signal that yields a graphic display, or tracing, 

in which the amplitude of the wire oscillation in millimeters 

is on the y-axis and the time in seconds is on 

the x-axis (Figure 2A). Amplitude is directly converted 

to physical units that represent the strength of the 

formed clot. 

Terminology 

Kol and Borjesson 

The TEG and ROTEM measure the same variables but 

utilize different terminology (Table 1). R or CT (clotting 

time) is the time in minutes from clot initiation until 

the first fibrin polymers are produced and the amplitude 

reaches 2 mm. K or CFT (clot formation time) is 

the time in minutes from the end of R until an amplitude 

of 20 mm is reached and represents the speed of 

clot formation. Alpha (a) is the angle in degrees tangent 

to the curve as K is reached and represents the 

406 Vet Clin Pathol 39/4 (2010) 405–416 c 2010 American Society for Veterinary Clinical Pathology

Kol and Borjesson Application of TEG to veterinary medicine 

Figure 2. Haemoscope TEG tracings using canine kaolin-activated blood. 

(A) Normal tracing. The x-axis represents time in minutes (min) and the yaxis 

the amplitude of pin rotation in millimeters. The tracing is completely 

symmetrical relative to the horizontal midline. R and K are the times that 

it takes for the tracing to reach the amplitudes of 2 and 20 mm, respectively. 

Alpha (a) is the angle of the slope in degrees (deg), representing 

acceleration of clot formation, and MA is the maximal amplitude of the 

tracing, representing the maximal strength of the clot. MA may be modified 

to physical units (G; dyne-s/cm 2 ) as follows: G dyn=cm 2 = (5000 MA)/ 

(100 MA). LY30, expressed as a percentage of MA, is the reduction in 

amplitude after 30 minutes and represents the percent of clot lysis. The 

result for each variable is found in row 3, and the reference intervals are 

in row 4. (B) Tracings indicating normocoagulable (green), hypocoagulable 

(blue), hypercoagulable (red), and secondary fibrinolytic (black) 

states. The result for each variable is found in rows 4–7, and the reference 

intervals are in row 3. 

acceleration/kinetics of fibrin formation and crosslinking. 

MA or MCF (maximal clot strength) is 

the maximum amplitude in millimeter and reflects 

maximal clot strength. G is the modification of MA 

to physical units. LY30/60 or CLI30/60 are the percent 

of clot lysis detected at 30 and 60 minutes, respectively, 

after MA is reached. A normal canine TEG tracing 

(Figure 2A) illustrates each variable, and examples 

of tracings that depict hypocoagulable, hypercoagulable, 

and secondary fibrinolytic states (Figure 2B) are 

provided. 

TEG Variables and Correlation with Routine 

Coagulation Assays 

Multiple studies have examined how the results of 

TEG analysis correlate with standard coagulation assays. 

20,22–25 Traditionally, the R time (Figure 2A) has 

been associated with soluble clotting factor activity. 20 

K time and a angle (Figure 2A) are nonspecific and 

have been associated with platelet concentration and 

function, fibrinogen concentration and function, and 

clotting factors activity. 20 The MA and G, a value calculated 

from MA and discussed together with MA, 

have been associated with platelet concentration and 

function and, to a lesser degree, with fibrinogen concentration. 

20 As TEG usage has increased, these previously 

ascribed correlations between TEG results and 

other hemostatic assay results (such as clotting factor 

activity and platelet concentration) have been modified. 

Although some studies have demonstrated a significant 

positive correlation between R time and 

prothrombin time (PT) or activated partial thromboplastin 

time (aPTT), these results could not be reproduced 

in other studies. 9,13,20,24–26 PT correlated with R 

time using rhTF-Haemoscope TEG in dogs admitted to 

an intensive care unit (ICU) and in healthy horses 13,26 ; 

however, there was no correlation between R time and 

PT or aPTT in healthy people or in people with 

Table 1. Nomenclature of selected thrombelastography (TEG) variables measured by the Haemoscope TEG and rotational thromboelastometry 

(ROTEM) analyzers. 

Variable Units Haemoscope TEG ROTEM 

Initiation time (time 0–2 mm amplitude) Minutes R CT (clot time) 

Clot kinetics (time 2–20 mm amplitude) Minutes K CFT (clot formation time) 

Clot kinetics (the slope between 2 and 

20 mm amplitude) 

Degrees a angle a angle 

Maximal clot strength and stability Millimeters MA (maximum amplitude) MCF (maximal clot strength) 

Maximal clot strength and stability Dynes/cm 2 

G — 

Clot lysis Percent LY30, LY60 CLI30, CLI60 



malignancies when using native or celite-activated 

Haemoscope TEG. 20 

Fibrinogen concentration has been shown to be 

highly correlated with G/MA and K time. This has been 

demonstrated utilizing various activators and methodologies, 

both in people and in various animals. 13,20,26–29 

In a group of human patients with solid tumors, hyperfibrinogenemia 

had a sensitivity and specificity of 

86.5% and 83.3%, respectively, for a ROTEM tracing 

indicating hypercoagulability. 27 Hyperfibrinogenemia is 

likely an independent risk factor for both venous and 

arterial thrombosis. 30,31 

Platelet concentration also correlates with G/MA 

and K time in dogs and in people. 20,22,26,29 The correlation 

between platelet count and G/MA was stronger 

after application of a logarithmic transformation to the 

platelet concentration. 22,24 We and others have noted 

that platelet concentration correlates with G and MA 

when platelet concentration is within the reference 

interval or decreased; however, thrombocytosis 

(4 400,000 platelets/mL) does not correlate with an 

increase in G and MA, 29 an observation consistent 

with the concept that whereas thrombocytopenia 

may contribute to a hemorrhagic phenotype, reactive 

thrombocytosis is not associated with hypercoagulability. 

32,33 

In human medicine, there is an association between 

increased D-dimer concentration, fibrinogen/ 

fibrin degradation products (FDPs), and increased 

TEG fibrinolytic variables (LY30 or CLI30; Table 1 and 

Figure 2B). 9,25,34 The TEG markers of hyperfibrinolysis 

may be superior to other laboratory measurements 

in human trauma and liver transplantation settings. 

9,25,34,35 To date, establishing similar correlations 

in veterinary medicine has had little success. 29 In 

dogs with experimentally induced thrombus formation, 

there was good agreement between TEG fibrinolysis 

variables, FDPs, thrombus size, and local blood 

flow at the site of the thrombus after fibrinolytic 

therapy. 36 However, in a recent case series of dogs 

with disseminated intravascular coagulation (DIC) 

and subsequent secondary fibrinolysis, there was no 

association between D-dimer concentration and 

increased rhTF-Haemoscope TEG fibrinolytic variables. 

29 Similar results were reported in a study in 

which human patients with severe sepsis, with or 

without overt DIC, had increased D-dimer concentration 

with no concurrent increase in ROTEM fibrinolytic 

markers using TF activation. 37 The latter 

findings are compatible with our experience, in which 

D-dimer concentration correlated poorly with kaolinactivated 

Haemoscope TEG variable, LY30 (unpublished 

data). 


Validation Studies and Preanalytical Factors 

In veterinary and human medicine, validation studies 

have been conducted to better characterize and define 

preanalytical and analytic factors that affect TEG variables. 

12–14,17,38–41 As with most hemostatic assays, preanalytical 

factors, including the delay between blood 

collection and analysis and the sample temperature, 

are important in TEG analysis. Blood for TEG analysis 

should be collected using a standardized protocol to 

minimize preanalytical variation. In several studies, a 

clinically acceptable intraassay coefficient of variation 

(CV) for the various Haemoscope TEG variables in dogs 

has been reported and varies from 3% to 18% depending 

on the variable. 12,17 Storage of blood for 120 minutes 

may result in a mild but significant trend toward 

a tracing that indicates hypercoagulability. 17,41 In 

horses, acceptable intraassay CVs of 1–12%, depending 

on the variable, were found when using both 

the Haemoscope TEG and ROTEM analyzers, 13,14,16 

although effects on results were noted as soon as 60 

minutes after blood collection in one study. 14 Blood 

samples refrigerated at 41C had decreased a angle and 

prolonged CT but also increased MCF, changes that are 

consistent both with hypocoagulability and hypercoagulability, 

respectively. 16 These findings are consistent 

with those noted in human medicine. In human 

medical practice, 120 minutes is an acceptable period 

of time between blood collection and TEG analysis 

with all variables having clinically acceptable CVs using 

various activators. 38–40 Variability in TEG results 

has also been attributed to differences between analyzers 

and operators. 13,38 These data indicate that TEG 

is valid for clinical use in dogs, horses, and cats although 

special attention should be given to minimize 

preanalytical factors, such as traumatic venipuncture, 

increased storage time, aberrant temperature, and in 

vitro hemolysis, as possible sources of error. 

In addition to preanalytical factors, red cell mass 

correlates with various TEG variables. Evidence suggests 

there is an inverse linear correlation between 

hematocrit and G/MA and a angle in people and various 

animal species. 16,20,42–46 Whether decreased red cell 

mass truly reflects in vivo hypercoagulability is subject 

to debate. 43,44,46,47 In people and dogs, decreased and 

increased hematocrit has been associated with hypercoagulability 

and hypocoagulability, respectively, in 

vivo. 16,20,42–46 Isolated reduction of hematocrit, in 

people, with no change in platelet concentration, coagulation 

factor concentration, or anticoagulant concentration 

accelerated blood coagulation, as demonstrated 

with celite-activated samples using the Haemoscope 

TEG and ROTEM. 44,46 Moreover, people with iron 



deficiency anemia and splenectomized thalassemic individuals 

had ROTEM tracings that were consistent 

with hypercoagulability. 43,44 However, a separate 

measure of hypercoagulability, the endogenous 

thrombin potential test, failed to provide supporting 

results. 43,44 Some authors have interpreted these data 

to suggest that decreased red cell density will result in 

an artifact in tracings that suggests hypercoagulability. 

However, others have argued that given the increased 

risk for thrombosis in thalassemic patients and the lack 

of increased potential for thrombin generation, 

the ROTEM may be superior to the plasma-based 

endogenous thrombin potential assay in detecting 

hypercoagulability that precedes thrombosis. In animals, 

increased hematocrit was associated with TEG 

variables indicative of hypocoagulability in Greyhound 

dogs and in transgenic mice with marked 

erythrocytosis. 42,45 In both studies, TEG tracings that 

indicated hypocoagulability were associated with 

hypocoagulable phenotypes, ie, an increased bleeding 

tendency. However, when the murine blood was diluted 

in vitro with maintenance of the platelet count, 

the TEG tracing normalized. 45 Induction of moderateto-severe 

in vitro hemolysis in canine and equine citrated 

blood samples resulted in significantly decreased 

G and MA values, consistent with hypocoagulability. 

16,48 This was attributed to in vitro platelet activation 

with resultant hyporeactive platelets contributing 

to decreased clot strength. 48 

Clinical Applications in Veterinary Medicine 

TEG has been studied in various clinical settings, 

mostly in dogs. Although recently validated for use in 

horses and cats, clinical studies have yet to be published 

outlining the clinical utility of TEG in these species. 

However, published abstracts suggest that the 

clinical use of TEG is being focused on critically ill foals 

and horses with colic. 49–51 There are sporadic reports of 

evaluation of coagulation in cattle, pigs, sheep, guinea 

pigs, rats, and various species of fish using TEG, 52–59 

but, to date there are no widely accepted guidelines to 

direct appropriate clinical use or interpretation of TEG 

tracings in these species. 

Hypercoagulable states 

VT is a serious and life-threatening complication of 

many underlying disease processes, including neoplasia, 

immune-mediated hemolytic anemia (IMHA), sepsis, 

heartworm disease, hyperadrenocorticism, and others; 

associated risk factors for the development of VT in animals 

are well described. 60–62 Routine hemostatic assays 

have poor sensitivity for the detection of hypercoagulability, 

5,26,29,63,64 and TEG has been evaluated for its 

capacity to provide early, sensitive detection of hypercoagulability. 

26,29,50,51,63–68 Discrepancies among studies, 

including variability of TEG methodology and the 

occasional absence of concurrent hematologic data, 

including platelet count, fibrinogen concentration, and 

hematocrit, limit our ability to fully interpret and compare 

TEG results among studies. Interpretation is further 

hindered by the absence of long-term prospective studies 

that confirm a positive correlation between TEG tracings 

that indicate hypercoagulability and true risk of 

thrombosis in the animal. To date, hypercoagulability, as 

evidenced by alterations in the TEG components G and 

MA, has been demonstrated in dogs with parvoviral enteritis, 

neoplasia, DIC, and IMHA and in dogs admitted 

to ICU. 26,29,63–65 

In an early case–controlled study, 9 puppies with 

naturally occurring parvoviral enteritis were compared 

with 9 age-matched control dogs. 63 Hypercoagulability 

was detected in all of the puppies with parvoviral 

entiritis, as evidenced by an increased MA using 

recalcified citrated blood. These puppies also had 

significantly increased fibrinogen concentrations 

compared with control puppies. Four of the dogs with 

parvoviral enteritis developed clinical evidence of 

catheter-associated VT or phlebitis. 63 

Underlying malignancy is considered a risk factor 

for thrombosis in animals and people. 60–62,69–73 The 

proposed mechanisms of thrombus formation are not 

fully characterized but may include altered plasmaor 

cell-based procoagulant or fibrinolytic activity, 

increased production of cytokines, including tumor 

necrosis factor, interleukin-1b, and vascular endothelial 

growth factor, by tumor cells, 72 aberrant TF expression, 

procoagulant factor production by neoplastic cells, and 

antiphospholipid antibody production. 72,74 In one study 

using rhTF-Haemoscope TEG, 67% of dogs with malignant 

neoplasia had hemostatic dysfunction, defined as 

an altered G value. Of these dogs, 75% were hypercoagulable 

and 25% were hypocoagulable. 64 Dogs with 

malignant neoplasia were significantly more likely to be 

hypercoagulable compared with dogs that had benign 

neoplasms, although 31% of the dogs with benign neoplasms 

were also hypercoagulable. 64 Hypercoagulability 

was not attributable to fibrinogen concentration as 

there was no significant difference in the fibrinogen 

concentrations of dogs with malignant compared with 

those with benign neoplasia. No information was provided 

on the overall correlation between fibrinogen 

concentration and G/MA or the number of dogs with 

TEG tracings indicative of hypercoagulability that developed 

VT. These findings are consistent with a similar 



study in which people with malignant neoplasms had 

increased G/MA values. 27 

TEG tracings that indicated hypercoagulable, 

normocoagulable, and hypocoagulable states were also 

found in dogs with DIC. In 50 dogs diagnosed with DIC 

based on a wide battery of hemostatic assays, tracings 

obtained using rhTF-TEG indicated that 22% were 

hypocoagulable, 34% were normocoagulable, and 

44% were hypercoagulable. 29 Interestingly, hypocoagulable 

dogs had a 2.4 times greater relative risk of 

death within 28 days than hypercoagulable dogs. The 

G value was concluded to best reflect the hemostatic 

status of dogs with DIC, and a TEG tracing indicating 

hypercoagulability was considered a favorable prognostic 

indicator. 29 In a similar study in human patients 

with severe sepsis with or without overt DIC, the 

ROTEM MCF value (equivalent to the MA value) in 

patients with severe sepsis did not differ significantly 

from the value in the healthy control group; however, 

patients with overt DIC had significantly decreased 

MCF, indicative of hypocoagulability. 37 

Hypercoagulability was also a common hemostatic 

abnormality in dogs admitted to an ICU with a variety of 

underlying disorders and in dogs with IMHA. 26,65 Eleven 

of 27 dogs in the ICU were classified as hypercoagulable 

by rhTF-TEG with supportive evidence that 

included decreased antithrombin activity and increased 

D-dimer concentration. 26 The majority of dogs with 

IMHA had TEG tracings, obtained using recalcified citrated 

blood, indicating hypercoagulability with only 6 of 

39 dogs classified as normocoagulable. 65 One potential 

confounding factor in the dogs with IMHA was that all 

dogs in the study were pretreated with corticosteroids, 

which are suspected to induce a hypercoagulable state 75 

and alter TEG variables. 68 The investigators claimed that, 

in this specific clinical setting, a TEG tracing indicating 

normocoagulability was a poor prognostic marker. 65 

Evidence in human clinical settings supports the 

hypothesis that a hypercoagulable state indicated by a 

TEG tracing is predictive of thromboembolic events, especially 

postoperatively. 18,76–78 Nonetheless, the data 

are not consistent. In a recent review paper, the predictive 

accuracy of TEG results for postoperative thromboembolic 

events was judged to be ‘‘highly variable,’’ 

and the authors recommended further prospective studies. 

76 Certainly in veterinary medicine, prospective studies 

are warranted to better characterize the effects of 

fibrinogen concentration, platelet concentration, and 

red cell mass on TEG tracings and to determine the sensitivity, 

specificity, positive predictive value, negative 

predictive value, and accuracy of TEG tracings that indicate 

hypercoagulability in predicting thromboembolic 

events in various clinical settings. 

Hypocoagulable states 


Accurate detection of hypocoagulability with resultant 

increased risk of hemorrhage could guide transfusion 

and hemostatic therapy during and after surgery or 

other invasive procedures, such as liver biopsy. Coagulation 

assays such as PT and aPTT, fibrinogen concentration, 

and platelet concentration are commonly used 

in both veterinary and human medicine to assess the 

risk of bleeding as a result of a diagnostic or surgical 

procedure. However, a poor correlation was found in 

people between prolonged PT and hemorrhage after 

invasive procedures, 4 leading to the conclusion that 

there was insufficient evidence to support the use of 

transfusion before procedures based on results of 

plasma-based hemostatic tests. 4 Similarly, in veterinary 

medicine, 2 retrospective studies have demonstrated 

variable correlation between coagulation test 

results and bleeding after fine-needle aspiration and 

tissue-core biopsy. 79,80 Given the poor capacity of 

these assays to predict bleeding, the use of TEG to accurately 

detect hypocoagulability and predict bleeding 

events has been evaluated. 

TEG may be superior to plasma-based assays in its 

capacity to correctly predict hemorrhagic episodes in 

dogs. 23,81,82 In a prospective study that compared the 

hemostatic phenotype in 27 dogs in hypocoagulable 

states, 27 in normocoagulable states, and 27 in hypercoagulable 

states based on results from rhTF-TEG, it was 

found that G value alone had a positive and a negative 

predictive value for bleeding of 89% and 98%, respectively. 

Moreover, G value more accurately predicted 

bleeding than the combination of platelet concentration, 

PT and aPTT results, D-dimer concentration, and 

fibrinogen concentration. 23 TEG results may also predict 

bleeding in dogs with severe factor VIII deficiency 

(hemophilia A). 81 In one study, bleeding was induced in 

anesthetized dogs with severe factor VIII deficiency and 

bleeding time was documented. The Haemoscope TEG 

component G, obtained using recalcified citrated blood, 

was superior to aPTT in predicting bleeding in vivo. 81 

TEG tracings showed incremental improvement associated 

with a dose-dependent response to therapy, 

whereas standard plasma-based assays failed to do so. 81 

TEG tracings may also be useful in monitoring hemostatic 

patterns and developing exercise regimens in dogs 

with severe hemophilia A; however, in this study, 

correlation of TEG results with hemostatic phenotype 

or bleeding tendency was not attempted. 82 Finally, a 

tracing indicating hypocoagulability, obtained by rhTF- 

TEG, was associated with a poorer prognosis and 

increased mortality risk in dogs admitted to ICU with a 

clinical suspicion of DIC. 29 These findings are supported 



by a new study in which a hypocoagulable state, based 

on kaolin-activated Haemoscope TEG tracings, in people 

admitted to ICU was an independent risk factor for 

death within 30 days. 83 

Monitoring anticoagulant therapy 

Low-molecular-weight heparin (LMWH) is increasingly 

being used in veterinary medicine for treatment of 

thromboembolic diseases and as thrombophylaxis in animal 

patients at increased risk for thrombosis. 84–88 Antifactor 

Xa activity is considered to be the ‘‘gold standard’’ 

for monitoring the effect of heparin on coagulability; 

however, this assay is expensive and not readily available. 

TEG has been assessed for its efficacy in monitoring 

heparin therapy in animal and human patients. 85,87–89 

In recent prospective studies, healthy dogs 21 and cats 19 

were given therapeutic doses of different heparins, including 

LMWH, subcutaneously. Only treatment with 

unfractionated heparin reached therapeutic levels as evidenced 

by anti-Xa activity and marked prolongation of 

Haemoscope TEG R time (recalcified method) with no 

clot formation up to 12 hours after a single subcutaneous 

administration. The in vitro effects of LMWH have 

also been tested on citrated canine blood. 87 TEG tracings 

showed dose-dependent prolongation of R and K times 

and decreased clot strength using rhTF-TEG and 

heparinase-coated cups, whereas TEG tracings using 

kaolin-activated TEG and heparinase-coated cups were 

unremarkable, except for a prolonged R time. 87 Similar 

results have been found in a recent study that explored 

the use of native Haemoscope TEG and heparinasecoated 

cups for monitoring LMWH for thrombophylaxis 

therapy in people with increased risk for deep vein 

thrombosis (DVT). 89 The authors suggested that concurrent 

measurement of Haemoscope TEG using plain and 

heparinase-coated cups may detect anticoagulated patients 

at increased risk of developing DVT; however, 

sensitivity, specificity, positive predictive value, and 

negative predictive value were not calculated. 89 To date, 

it appears that TEG may have some clinical utility for the 

monitoring heparin therapy in animals; however, expected 

TEG results will depend on the choice of activator, 

the choice of plain or heparinase-coated cups, and 

the dose and type of heparin used. 

Platelet function 

Congenital and acquired disorders of platelet dysfunction 

are well characterized and relatively common in 

animals and have been reviewed. 90–92 Acquired platelet 

dysfunction can occur secondary to uremia, infection 

with various agents, such as Ehrlichia canis and 

FeLV, snake envenomation, neoplasia, liver disease, 

and drug administration, especially nonsteroidal antiinflammatory 

drugs (NSAID). 92–98 The use of specific 

platelet inhibitor drugs, such as clopidogrel (platelet 

ADP chemoreceptor [P2Y 12] inhibitor), and glycoprotein 

(GP) IIb/IIIa inhibitors may predispose animals to 

bleeding. As such, there is interest in platelet function 

assays that are readily accessible, reliable, and costeffective 

for monitoring antiplatelet therapy or diagnosing 

congenital or acquired platelet disorders. 99,100 

Platelets have multiple physiologic activators and 

are a major contributor to the TEG G/MA value. 

Thrombin is a major and powerful platelet activator, 

and its presence masks the detection of platelet dysfunction 

that results from alteration of pathways of 

weaker activators, such as ADP or collagen. 101 Sporadic 

studies have shown that TEG tracings did not differ between 

normal dogs and dogs with either a specific platelet 

dysfunction, such as Scott syndrome, or dogs that 

were treated with NSAID. 102,103 Haemoscope TEG 

PlateletMapping is a modified TEG assay specifically designed 

to asses platelet function. 101 The concept behind 

PlateletMapping is to eliminate the potent effect of 

thrombin on blood platelets during clot formation. 

Blood is drawn into heparin and further activated with 

reptilase and factor XIIIa to allow a small, polymerized 

fibrin clot to form in the absence of thrombin. The clot 

serves as a scaffold for platelet activation. Two other 

TEG cups are used and platelet agonists, ADP and 

arachadonic acids, are added to induce platelet activation. 

A fourth heparinase-coated TEG cup and kaolin 

activation are also used. Equations are derived to assess 

the percent MA aggregation response to an agonist. 

Haemoscope TEG PlateletMapping showed good correlation 

with optic platelet aggregometry in detecting 

platelet dysfunction after in vitro inhibition by antagonists 

of various platelet receptors, such as GP IIb/IIIa, 

P2Y 12, and thromboxane A 2 receptor. 101 Preliminary 

data suggest that Haemoscope TEG PlateletMapping 

may be used to assess platelet inhibition in dogs that 

are treated with clopidogrel. 104 The primary uses to date 

for TEG PlateletMapping include monitoring platelet 

inhibition therapy and diagnosing naturally occurring 

thrombocytopathies; however, this novel technique 

may also be able to identify platelet hyperreactivity. 105 

Recently, PlateletMapping was also validated for use in 

ROTEM analyzers. 106 

Summary 

TEG is an old technique being used in new ways to advance 

our understanding of hemostasis. TEG has been 



validated in dogs, horses, and cats. TEG analysis should 

be performed on citrated blood by experienced personnel 

using standard protocols in which preanalytical 

factors, including storage temperature and time 

to analysis, are controlled. Reference intervals 

should be generated locally using specific activators. 

Hematologic measurements that may confound TEG 

analyses, including fibrinogen concentration, platelet 

concentration, and RBC mass, should be considered 

when interpreting TEG results. We believe that 

TEG analysis provides complementary information to 

routine coagulation assays. Additional long-term 

prospective studies are needed to determine whether 

TEG can be used to (1) guide and monitor blood 

product transfusion and anticoagulant therapy or (2) 

accurately predict severe clinical complications associated 

with disruptions in hemostasis, including thrombosis 

and hemorrhage. 

Disclosure: The authors have indicated they have no affiliations 

or financial involvement with any organization or entity 

with a financial interest in, or in financial competition 

with, the subject matter or materials discussed in this paper. 

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