Introduction

• Coagulation abnormalities encompass a myriad of disorders that affect both the ability to form stable blood clots and the controlled degradation of blood clots (fibrinolysis).
• Coagulation abnormalities may be congenital in nature Hemostatic disorders: inherited (eg hemophilia , von Willebrands disease) or acquired Hemostatic disorders: acquired (eg vitamin K antagonist rodenticide intoxication Anticoagulant rodenticide poisoning, disseminated intravascular coagulopathy Disseminated intravascular coagulation). The severity of bleeding abnormalities may also range from subclinical to life-threatening.
• Recognition of coagulation abnormalities often involves the detection of clinical signs compatible with either spontaneous bleeding or in some cases, thrombosis. The most commonly encountered clinical signs indicative of bleeding tendencies are petechiation, ecchymoses, hematoma formations and epistaxis. The most common manifestations of thrombosis include aortic thromboembolism in cats Thromboembolism: aorta and pulmonary thromboembolism in dogs with immune-mediated hemolytic anemia Anemia: immune-mediated hemolytic.
• Typical investigations for clotting disorders include manual platelet counts Hematology: platelet count, assessment of buccal mucosal bleeding time Buccal mucosal bleeding time and assaying activated clotting time Hematology: activated clotting time, prothrombin time Hematology: prothrombin time and activated partial thromboplastin time Hematology: activated partial thromboplastin time.
• Although each test has its advantages and disadvantages, the major limitation with most clotting assays is they each only assess a small facet of the coagulation pathways. Often one must perform a series of clotting assays to gain a better understanding of the coagulation status of a particular patient. Another limitation is virtually all conventional tests are designed only to detect abnormalities in clot formation, ie hypocoagulable states.
• There are tests that may give an assessment of hypercoagulability but unfortunately these assays (eg fibrin(ogen) degradation products (FDP Fibrin degradation products) and D-dimers Hematology: D-dimers) only give a non-specific and indirect indication of fibrinolysis rather than a true assessment of thrombotic risk.
• As coagulation disorders are increasingly being recognized as important aspects of many diseases in veterinary species, the need for better tools to assess coagulation has been recognized. Moreover, the ability to assess clot formation, thrombotic risk and thrombolysis are all highly desirable.
• Thromboelastography (TEG) is an analytic method that enables a more global assessment of coagulation in whole blood. This assay may be done on-site with results available within one to two hours of processing. An advantage TEG holds over all other methods of assaying hemostasis is the ability to assess clot initiation, amplification, propagation, and fibrinolysis.
• As TEG is performed on whole blood one can also assess the interactions of platelets with clotting proteins, as well with red and white blood cells. Thus TEG combines evaluation of plasma components of coagulation with cellular components, a feature of coagulation that cannot be assessed by other currently clinically available methods.

Methodology

Application of TEG in assessing clinical patients

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.
• Donahue S M, Otto C M (2005) Thromboelastography: A tool for measuring hypercoagulability, hypocoagulability, and fibrinolysis. Journal of Veterinary Emergency Critical Care 15 (1), 9-16 VetMedResource.
• Wiinberg B, Jensen A L, Rojkjaer R et al (2005) Validation of human recombinant tissue factor-activated thromboelastography on citrated whole blood from clinically healthy dogs. Vet Clin Pathol 34 (4), 389-393 PubMed.
• Alwood A J, Downend A B, Slensky K A et al (2004) Evaluation of thromboelastography (TEG) in normal cats. J Vet Emerg Crit Care 14 (S1), S1-17 Wiley Online Library.
• Otto C M, Rieser T M, Brooks M B et al (2000) Evidence of hypercoagulability in dogs with parvoviral enteritis. JAVMA 217 (10), 1500-1504 PubMed.