Evaluation of a modified thrombelastography assay initiated with recombinant human tissue factor in clinically healthy horses

Abstract

Background: Thrombelastography (TEG) is used to evaluate the viscoelastic properties of blood during clotting and provides a global assessment of hemostasis and clot lysis. TEG analysis initiated with recombinant human tissue factor (TF) has not been evaluated in clinically healthy horses. Objectives: The purpose of this study was to determine whether TEG results are affected by the time elapsed between sampling and analysis (storage time) of equine blood samples and to establish a preliminary equine reference interval for a modified TEG assay, using recombinant human TF to initiate coagulation. Methods: Citrated blood samples were obtained from 20 clinically healthy adult horses. Thirteen samples were stored for 30, 60, and 120 minutes at room temperature before TEG analysis. Coagulation was initiated by adding 20 mL of CaCl 2 to 330 mL of blood and 10 mL of diluted recombinant TF for a final dilution of 1:3600. Reaction (R) and clotting (K) times, angle (a), and maximum amplitude (MA) were compared between time points. A preliminary reference interval (minimum-maximum values) was determined using data from all 20 horses after 30 minutes of sample storage. Results: There was a significant effect of storage time on R, K, and a but not MA. Reference intervals were: R, 3.65-6.4 minutes; K, 1.8-5.45 minutes; a, 33.4-66.21; MA, 41.2-64.1 mm; lysis at 30 minutes post-MA (LY30), o 2.75%; and lysis at 60 minutes post-MA (LY60), 1.55-9.5%. Conclusions: TEG can be performed on equine citrated blood samples using recombinant human TF to activate clot formation. TEG parameters were significantly affected by storage time, suggesting an incomplete inhibition of coagulation in citrated blood.While conventional coagulation tests evaluate the soluble or plasmatic components of coagulation, in vivo coagulation is the sum of complex interactions among coagulation factors, platelets, endothelial cells, erythrocytes, and even leukocytes.1,2 Thrombelastography (TEG) assesses the mechanical properties of the blood clot during its formation and subsequent lysis. [3][4][5] In human medicine, TEG is used to detect clinically significant coagulation disorders in patients perioperatively and in intensive care.6 TEG is commonly performed on native fresh whole blood within 5 minutes of collection.7 This constraint limits its use in clinical pathology laboratories and in many veterinary hospital facilities. More recently, the use of citrated whole blood has extended the time that may lapse between blood collection and initiation of coagulation. 7,8 TEG has been validated and used to predict the risk of bleeding and assess hypercoagulability in dogs [9][10][11][12] and has been used to monitor heparin therapy in cats.13 TEG also was used to evaluate a horse with a platelet dysfunction.14 Horses, like other species, can have congenital and acquired coagulation disorders 15 and TEG could be useful in the rapid diagnosis of coagulopathies associated with gastrointestinal disorders or neonatal sepsis. 16,17 The objectives of this study were to as...

Operator‐based variability of equine thromboelastography

“…All α values outside the reference range yielded a hypercoagulable reading (more acute angles, signifying more rapid clot formation). Erroneously increased α has been associated with prolonged sample storage times and low PCV . The majority of the abnormal MA values trended toward hypocoagulability in the current study, where lower MA values indicate weaker overall MA.…”

“…Although TEG kits and standardized, commercially available evacuated tubes containing anticoagulant were used, small variations in the blood volumes collected and in the amount of anticoagulant or reagents cannot be completely excluded, and may have affected TEG results in this study. All TEG analyses were performed between 35 and 45 minutes after sample collection to eliminate the effects of prolonged storage on TEG values …”

Evaluation of kaolin-activated thromboelastography and sample stability in healthy horses

“…Since horses with acute illnesses that require immediate coagulation testing (e.g., colic) can be admitted in the evening or during the night, inconsistencies among receiving clinicians and operators of blood sample analysers in clinics mean that methods that are least influenced by preanalytical factors should be selected. A few studies have described thromboelastography in horses and a few used kaolin-activated TEG (Epstein et al 2009;Leclere et al 2009). To our knowledge, there is only one study evaluating kaolin-activated TEG in healthy horses.…”

Application of thrombelastography/thromboelastometry to veterinary medicine

“…TEG results guide administration of blood products and anticoagulants and predict hemorrhage during surgery and postoperatively 9,10 . In veterinary medicine, TEG and ROTEM have been validated for use in dogs, horses, and cats 11–17 …”