Thromboelastography: Measuring Blood Coagulation in Real Time

The development of thromboelastography (TEG) in 1948 is credited to Dr. Helmut Hartert, who was working at the University of Heidelberg in Germany at the time.¹ Also called a “viscoelastic assay,” this non-invasive test assesses the entire process of clot formation and dissolution by measuring the viscosity and elasticity of a whole blood sample during clotting under low shear stress (see FIGURE). It does this via a continuously applied rotational force on the blood sample that is transmitted to an electromechanical transduction system. The output, then, is a graph that shows qualitative and quantitative dynamic measures of the functions of many of the proteins and other blood factors, including fibrinogen, microvesicles, platelets, and other cellular blood components such as white blood cells.²

FIGURE. Thromboelastography (TEG): Principles and Interpretation

v1.2, 2020-10-27, by Nick Mark, MD/onepagericu.com; CC BY-SA 3

“Basically, TEG uses mechanical rotation to detect the global dynamics of blood clot formation,” said Hui Yin Lim, MBBS, a laboratory and clinical hematologist at Northern Hospital in Melbourne, Australia. The activated partial thromboplastin time (aPTT) and prothrombin time (PT) tests provide information on the time it takes for clot formation and assay anticoagulation levels.

“The aPTT and PT tests are about 5% of clot formation, while TEG looks at the dynamics of clot formation from clot initiation, propagation, and clot lysis. This gives you the whole blood clotting picture,” Dr. Lim explained.

ASH Clinical News spoke with Dr. Lim and other experts about what TEG is, its benefits and drawbacks, and how it is used in clinical practice in comparison with other coagulation tests.

A Point-of-Care Test

The first reported clinical use of TEG was to guide blood component therapy for wounded soldiers during the Vietnam War.³ Gradually, studies and practice showed that TEG was useful for patients undergoing liver transplant⁴ and to monitor patients during cardiac surgery.⁵ Demonstrations of the clinical utility of TEG have grown in the past few decades, and TEG devices are now used as a point-of-care test in hospitals around the world to assess coagulation and which components of the hemostatic system are impaired to guide transfusion.

TEG is often used in transfusion medicine and during cardiac surgery when a 10- to 15-minute analysis provides information on a patient’s coagulation status at the operating table and in trauma patients. The TEG and rotational thromboelastometry (ROTEM) systems are also increasingly used in maternal-fetal medicine to assess the global clotting potential in women who may have factor deficiencies, such as factor XI deficiency, in which factor levels may not always correlate with bleeding risk, said Homa K. Ahmadzia, MD, assistant professor in the Department of Obstetrics & Gynecology and the Division of Maternal-Fetal Medicine at George Washington University in Washington, DC.

“For such patients, a multidisciplinary care team from hematology, transfusion medicine, obstetric anesthesia, and maternal-fetal medicine are involved and decide together what preventative interventions will be used at delivery or what management we’ll use if a postpartum hemorrhage is identified,” she said.

For other high-risk obstetrics patients who may not have known risk factors and who experience severe postpartum hemorrhage, Dr. Ahmadzia and her colleagues use TEG to help guide transfusion of blood products such as fresh frozen plasma or fibrinogen concentrate. 

Awareness and Availability

Not all hospitals have viscoelastic testing devices.

“It really depends on whether the hematologists and anesthetists have an interest in these tests,” Dr. Lim said. “Technicians need to be trained to use the machines and clinicians need to learn to interpret the test results correctly.”

Dr. Lim and Maha Othman, MD, PhD, professor in the Department of Biomedical and Molecular Sciences and a hematologist by training who runs a thrombosis research laboratory at Queen’s University in Ontario, encourage their colleagues to procure a TEG or ROTEM analyzer and learn how to use and interpret the tests. TEG isn’t exactly inexpensive, but it does reduce the need for blood products, which can be expensive and hard to come by, and it can also reduce the costs related to surgical re-exploration, Dr. Lim said.

For TEG to be used more widely, Dr. Othman said, “It’s the awareness among clinicians, understanding of test applicability, and interpretation that are needed, and ultimately large studies to validate the clinical efficacy.”

Benefits and Drawbacks

A meta-analysis of 17 randomized controlled cardiac surgery trials showed that the use of TEG decreased blood product transfusions and surgical re-exploration due to postoperative bleeding, including lower incidence of acute kidney injury and thromboembolic events.⁶ In the diagnosis of coagulopathy in cardiac surgery, TEG was also found to be more cost effective compared to standard coagulation tests.⁷

A major benefit of TEG is its use during surgery, providing a global picture of coagulation, which conventional coagulation tests cannot provide. The device can be in the operating room and, if necessary, can provide coagulation results within 10 to 15 minutes for a patient who is bleeding, which can guide the use of specific transfusion products. Comparatively, results from conventional fibrinogen and D-dimer tests can take several hours to obtain.

Another benefit is that TEG uses whole blood. For conventional tests, the blood sample is separated and only the plasma component is used for analysis.

“The advantage of using whole blood in TEG is that platelets, white blood cells, and even red cells contribute to blood clotting, making it more physiologically relevant than a plasma test,” Dr. Othman said.

The portability of the TEG device, compared to laboratory coagulation testing, is also a major advantage. According to Dr. Lim, “The newer TEG instrument can potentially be part of the arsenal in a medical emergency vehicle or a rescue helicopter where you cannot run conventional coagulation tests because those require grounded machines in a laboratory.”

While TEG does reduce the need for transfusion, whether the test reduces mortality among patients undergoing cardiac surgery is still unclear. One systematic review of 17 randomized studies that included 1,493 patients undergoing cardiac surgery showed that TEG or ROTEM decreased transfusion of blood components and reduced overall mortality, yet the quality of the included studies was considered low.⁸

“In transfusion medicine in trauma and surgery, TEG has been demonstrated to lead to faster and reduced administration of blood products with better outcomes, so I think there is a definite role there,” said Alfred Lee, MD, PhD, associate professor of medicine and hematology at the Yale Medical School in New Haven, Connecticut.

Dr. Lee noted that he was excited when his institution implemented TEG testing, but his enthusiasm waned when he learned through trial and error that there are instances when TEG may not affect clinical decisions.

“In many settings, it’s hard to take the results from TEG and apply them,” he said. “As an example, I’ve sent TEGs in a lot of patients with abnormal bleeding histories, whom I’ve suspected of having a bleeding diathesis that cannot be identified using traditional laboratory measures. In many of those cases, the TEG results are normal, while in some, the TEG results suggest hypercoagulability or the higher tendency to clot. There’s not really any way to apply this knowledge clinically.”

The widespread use of viscoelastic assays in maternal-fetal medicine, including in the delivery room, will depend on additional studies demonstrating utility and benefit. The rapidness of the timing from blood draw to test result, without the need to separate out plasma for conventional coagulation testing, is a big advantage, according to Dr. Ahmadzia. One drawback of TEG she noted is that the reference coagulation ranges are not universally adopted for pregnancy and that multi-disciplinary care is needed to analyze TEG results, which may not always be available in smaller hospital systems. Still, there are some relatively new recommendations.

The International Society on Thrombosis and Haemostasis (ISTH) Scientific and Standardization Committee, focusing on women’s health, released recommendations on the use of TEG and ROTEM in the field of obstetrics.⁹ They are based on an extensive systematic review of 93 studies, including two randomized clinical trials.¹⁰

Dr. Ahmadzia continues to conduct trials that test the utility of viscoelastic assays in maternal-fetal medicine. Recently, she and her colleagues used a modified version of the ROTEM assay to measure the pharmacodynamics of tranexamic acid among pregnant women at the time of cesarean delivery to determine the optimal dose of tranexamic acid as prophylaxis needed to prevent postpartum hemorrhage.¹¹

“This is a useful technology to apply in translational research that deals with coagulation at the time of delivery,” Dr. Ahmadzia said.

In general, Dr. Othman attributes limited use of viscoelastic assays to the lack of clinical guidelines on their use in any patient population, which she sees as a major drawback.

“We have not been able to write these guidelines because we did not have sufficient results from robust clinical studies,” she said. “Most of the evidence on TEG is from observational, single-center studies, and small studies, unfortunately.”

COVID-19 and Future Use

Besides its value in identifying bleeding in patients, TEG has also been shown to be effective for detecting hypercoagulability and cancer-associated thrombosis.^12,13 As thrombosis is a major contributor to death in patients with severe coronavirus infection, the disruption of coagulation among patients with COVID-19 can potentially be monitored using TEG or ROTEM.

“The key goals for the use of TEG or ROTEM would be to assess and predict the occurrence of venous thromboembolism and distinguish among severe and moderate cases,” Dr. Othman said.

There are a couple of small studies on the use of these tests that show the assays can predict a hypercoagulable state.^14,15

“But we don’t know how this translates to clinical practice just yet,” Dr. Lim said.

According to Dr. Lee, there are researchers who are trying to use TEG to identify patients with long COVID, who may have a hypercoagulable phenotype, to potentially target those patients for specific treatments. “This sounds exciting, but we are still awaiting the data,” he said.

Although there remains much research to be done, specific settings seem more conducive to TEG use than others. More applications may yet be determined in the future.

“In 2022, with all the advancement in viscoelastic testing technology, TEG and ROTEM have become quite easy to use,” Dr. Lim said. “I think this test has its place in medicine, especially with emerging evidence supporting its use in settings such as cardiac surgery and trauma. It would be something that clinicians in all hospitals should be trying to implement into clinical day-to-day practice in appropriate settings.”

References

1. Hartert H. Blood clotting studies with thrombus stressography; a new investigation procedure. Klin Wochenschr. 1948;26(37-38):577-583.
2. Selby R. “TEG talk”: expanding clinical roles for thromboelastography and rotational thromboelastometry. Hematology Am Soc Hematol Educ Program. 2020;2020(1):67-75.
3. Hardaway R, Bredenberg C. Monitoring hematology laboratory values. In: Care of the Wounded in Vietnam. Manhattan, Kansas: Sunflower University Press; 1989.
4. Kang YG, Martin DJ, Marquez J, et al. Intraoperative changes in blood coagulation and thrombelastographic monitoring in liver transplantation. Anesth Analg. 1985;64(9):888-896.
5. Shore-Lesserson L, Manspeizer HE, DePerio M, Francis S, Vela-Cantos F, Ergin MA. Thromboelastography-guided transfusion algorithm reduces transfusions in complex cardiac surgery. Anesth Analg. 1999;88(2):312-319.
6. Deppe A-C, Weber C, Zimmermann K, et al. Point-of-care thromboelastography/thromboelastometry-based coagulation management in cardiac surgery: a meta-analysis of 8332 patients. J Surg Res. 2016;203(2):424-433.
7. Whiting P, Al M, Westwood M, et al. Viscoelastic point-of-care testing to assist with the diagnosis, management and monitoring of haemostasis: a systematic review and cost-effectiveness analysis. Health Technol Assess. 2015; No. 19.58.
8. Wikkelsø A, Wetterslev J, Møller AM, Afshari A. Thromboelastography (TEG) or rotational thromboelastometry (ROTEM) to monitor haemostatic treatment in bleeding patients: a systematic review with meta-analysis and trial sequential analysis. Anaesthesia. 2017;72(4):519-531.
9. International Society on Thrombosis and Haemostasis. Review of viscoelastic testing (TEG/ROTEM) in obstetrics and recommendations from the women’s health SSC of the ISTH. Accessed April 18, 2022. https://cdn.ymaws.com/www.isth.org/resource/resmgr/subcommittees/homa_k._ahmadzia_dec_15,2019.pdf.
10. Amgalan A, Allen T, Othman M, Ahmadzia HK. Systematic review of viscoelastic testing (TEG/ROTEM) in obstetrics and recommendations from the women’s SSC of the ISTH. J Thromb Haemost. 2020;18(8):1813-1838.
11. Ahmadzia HK, Luban NLC, Li S, et al. Optimal use of intravenous tranexamic acid for hemorrhage prevention in pregnant women. Am J Obstet Gynecol. 2021;225(1):85.e1-85.e11.
12. Walsh M, Moore EE, Moore H, et al. Use of viscoelastography in malignancy-associated coagulopathy and thrombosis: a review. Semin Thromb Hemost. 2019;45(4):354-372.
13. Toukh M, Siemens DR, Black A, et al. Thromboelastography identifies hypercoagulablilty and predicts thromboembolic complications in patients with prostate cancer. Thromb Res. 2014;133(1):88-95.
14. Salem N, Atallah B, El Nekidy WS, Sadik ZG, Park WM, Mallat J. Thromboelastography findings in critically ill COVID-19 patients. J Thromb Thrombolysis. 2021;51(4):961-965.
15. Panigada M, Bottino N, Tagliabue P, et al. Hypercoagulability of COVID-19 patients in intensive care unit: a report of thromboelastography findings and other parameters of hemostasis. J Thromb Haemost. 2020;18(7):1738-1742.