Effects of Hematocrit on Thromboelastography Tracings in Dogs
ACVIM 2008
P. Vilar; J. Hansell; N. Westendorf; M.C. Iazbik; L. Marín; C.G. Couto
The Ohio State University, Veterinary Clinical Sciences
Columbus, OH, USA

The main advantage of the TEG compared to other conventional tests of hemostasis (e.g., bleeding time [BT], prothrombin time [PT], activated partial thromboplastin time [aPTT], D-Dimer) is the ability to assess ex vivo using a whole blood sample, most of the in vivo components that play a role in the formation of the hemostatic plug (i.e.,; red blood cells [RBCs], white blood cells, platelets, clotting factors, fibrinolytic proteins). Since RBCs are the major component of blood, the hematocrit (HCT) is the main factor that influences blood viscosity. Flow and/or rheological conditions of the blood affect coagulation (Kretschmer V et al 2004); and, by definition, TEG evaluates the viscoelastic properties of the clot. Therefore, our objective was to evaluate the effects of HCT on TEG parameters in order to correctly interpret the TEG tracings in patients with high or low HCT values (e.g., blood loss anemia, DIC, Greyhounds). Nine healthy dogs based on results of physical examination, complete blood count (CBC), clotting times (aPTT, PT), fibrinogen concentration, and TEG, with no previous history of bleeding disorders were included in the study. Blood samples were collected by jugular venipuncture using a butterfly collection set, and aliquoted into three 2.7 ml Vacutainer 1:9 collection tubes containing 3.2 % buffered sodium citrate. Two citrate tubes were centrifuged immediately to obtain platelet rich plasma (PRP) used to serially dilute the pure red blood cell samples (PRBC's) to obtain final HCT values of 60%, 40%, and 20% in each dog; the platelet counts were maintained within the reference range (130-450 x 109 u/L) by using PRP.A single recalcified (20 µLCaCl2) citrated native TEG test per sample was performed. Five specific TEG parameters were compared: The "R" is the time from addition of the agonist (CaCl2) until the clot starts forming; "K" or clot kinetics; angle or "α", is related to the fibrinogen concentration and fibrin build-up and cross-linking; "MA" or ultimate strength of the clot formation and finally "G" represents the elastic shear of the clot. The Pearson's correlation coefficients (r) for HCT and TEG parameters were: "R"= 0.85; "K"= 0.24; angle= -0.99; MA = -0.99; and G= -0.81.

In conclusion HCT showed a strong correlation with some of the TEG parameters when PLT count was within the normal limits. Therefore, HCT values should be addressed in order to obtain a correct interpretation of the TEG tracings in dogs.

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Paulo Vilar Saavedra

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