Objectives – To develop a standardized technique for thrombelastography (TEG) analysis in healthy adult horses, with and without the ex vivo addition of tissue factor (TF) as an activator. To determine reference intervals for TEG parameters in the horse, and to determine if traditional coagulation tests correlate with TEG.
Design – Prospective, observational.
Setting – Veterinary teaching hospital.
Animals – Twenty-six healthy adult horses.
Interventions – None.
Measurements and Main Results – Thrombelastography with (TF-TEG) and without (TEG) the addition of TF performed by 4 operators. Coagulation profiles (prothrombin time, activated partial thromboplastin time, platelet count, fibrinogen, antithrombin, and fibrinogen degradation products) were assessed in a subset of horses. Mean values (SD) for TEG parameters in healthy horses were: reaction time (R)=17.0 minutes (3.0 min), K time (K)=5.8 minutes (2.3 min), clotting rate (Ang)=42° (14°), maximum clot strength (maximum amplitude [MA])=60.3 mm (5.7 mm), CL30=97.0% (2.0%), LY30=0.8% (0.6%), CL60=92% (5.9%), LY60=3.2% (2.5%). Mean values (SD) for TF-TEG parameters were: R-TF=6.6 minutes (1.4 min), K-TF=3.1 minutes (1.0 min), Ang-TF=50.9° (9°), MA-TF=62.3 mm (5.1 mm), CL30-TF=97.8% (1.6%), LY30-TF=0.6% (0.5%), CL60-TF=90.8% (4.2%), and LY60-TF=3.6% (1.9%). The addition of TF decreased R and K and increased Ang. TF-TEG had a narrower SD for R, K, Ang, CL60 and LY60 compared with TEG. Interoperator differences were reduced by the addition of TF. Regression analysis indicated a positive relationship between MA and fibrinogen concentrations (P=0.02) and R-TF time and prothrombin time (P=0.03).
Conclusion – TF-TEG using the described protocol may minimize variability in data obtained across institutions or users. However, due to the variability associated with different operators, it is recommended that each laboratory set up individual reference intervals with the personnel who will perform the assay, and that the assay protocols and data obtained are compared on a regular basis.