Thromboelastography
Thromboelastography (TEG) analysis is a viscoelastic measurement technique used to assess global clot formation and lysis in whole blood. It is sometimes termed rotational TEG; a similar measurement technique is ROTEM (rotational thromboelastometry).
The advantage of TEG analysis over traditional minimum coagulation panels consisting of platelet count, PT, and activated PTT testing is that TEG can detect hypercoagulable states and increased fibrinolysis (Fig. 27.2). TEG is therefore the only readily available test of hypercoagulability in veterinary medicine. Fibrinolysis can be assessed by D-dimer in horses or by FDPs in other large animal species, but with the specificity issues inherent to FDP testing as described earlier. Disadvantages of TEG or ROTEM testing include the need for analysis within 2 hours of blood collection and the impact of marked anemia on testing.52,53 Substantial thrombocytopenia can alter TEG results, but the results may be useful as a potential index of bleeding tendency in the patient and may be superior to platelet count alone for this use because TEG also accounts for platelet function.54,55 A concurrent CBC is vital for interpretation of TEG results.Studies have shown some diagnostic and prognostic utility of TEG in evaluating coagulation in horses with gastrointestinal disease.56-58 Using TEG and other viscoelastic testing, studies in neonatal foals have determined both that coagulation parameters in normal neonatal foals can differ from those in adult horses and that septic foals can have evidence of coagulation abnormalities, including hypercoagulability.59,60 Other common uses of TEG or ROTEM in large animal research studies include evaluation of the effects of plasma or artificial colloid transfusion on coagulation and assessment of the effects of dexamethasone treatment in healthy adult horses (no differences seen) and in veal calves (treated calves had evidence of hypercoagulability).61-65