Critical Factors Contributing to the Thromboelastography Trace Stephen G. MacDonald, M.Phil., 1 and Roger J. Luddington, Ph.D. 1 ABSTRACT The thromboelastography trace provides a graphical and numerical representation of the viscoelastic changes associated with fibrin polymerization. When used with whole blood, the shape of this trace is a composite of the effects of white and red cell content and composition, platelet number and function, fibrinogen concentration, as well as coagu- lation protein function and balance. The trace is also influenced by pharmacological agents such as anticoagulants, antiplatelet therapy, and coagulation factor supplementation. As such the main role of this technology has been as a point-of-care device to guide transfusion of blood components. Recently the technology has moved from the cardiac and hepatic surgical settings, where most of the early work was focused, into other areas of hemostatic monitoring. New applications for pharmaceutical monitoring and patient screening are being explored. This review gives a broad overview of the applications of the technology. In particular it considers the factors that most influence the characteristics of the trace, be they preanalytical, analytical, or clinical. KEYWORDS: Thromboelastography, thromboelastometry, hemostasis, global screening. Thromboelastography was first described >60 years ago. 1 Since then, several variants have evolved. Several coagulation monitoring devices are now on the market that assess the viscoelastic properties of blood including the Thromboelastograph (TEG) (Haemo- scope Corporation, Niles, IL), the ROTEM (Penta- pharm GmbH, Munich, Germany), and the Sonoclot analyzer (Sienco Inc., Arvada, CO). They provide graphical representations of the dynamics of fibrin poly- merization in citrated or noncitrated whole blood, pla- telet-rich or platelet-poor plasma, with or without activation. The process is displayed in real time and provides numerical data for such parameters as time to clot, rate of formation of the clot, strength of the clot, and stability of the clot along with assessment of fibri- nolysis. To interpret viscoelastic hemostatic assays (VHAs), the components of the trace and the different terminology used need to be understood (Fig. 1). These technologies employ a sample cup and a centrally placed pin/probe that form the reaction cham- ber. Fibrin polymerization is either detected by progres- sive restriction of the oscillation of the cup (TEG), a detector pin submerged in the reaction chamber (RO- TEM), or restriction of the vertical oscillation of the probe (Sonoclot). This review concentrates on factors affecting the thromboelastograph/thromboelastogram trace produced by the TEG/ROTEM. As with all tests of hemostasis, published data should be reviewed in light of the assay variant used and the stated normal range of the testing center. This 1 Haemostasis Unit, Haematology Department, Addenbrooke’s Hospital, Cambridge, United Kingdom. Address for correspondence and reprint requests: Roger Luddington, M.Phil., Ph.D., Haemostasis Unit, Haematology Department, Addenbrooke’s Hospital, Part of Cambridge University Hospitals NHS Foundation Trust, Cambridge, CB2 0QQ, United Kingdom (e-mail: Roger.luddington@addenbrookes.nhs.uk). Global Hemostasis: New Approaches to Patient Diagnosis and Treat- ment Monitoring; Guest Editor, Maha Othman, M.D., Ph.D. Semin Thromb Hemost 2010;36:712–722. Copyright # 2010 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662. DOI: http://dx.doi.org/10.1055/s-0030-1265288. ISSN 0094-6176. 712 Downloaded by: Northwestern University. Copyrighted material.