New Standards for Evaluating Blood Clotting in Horses

New Standards for Evaluating Blood Clotting in Horses

Drs. Pamela Wilkins (left) and Maureen McMichael determined that horses' blood differs substantially from that of humans and dogs when thromboelastometry is used to assess the status of blood flow and coagulation.

Photo: University of Illinois College of Veterinary Medicine

Two University of Illinois faculty members who are boarded in veterinary emergency and critical care recently published their findings showing that the blood of horses differs substantially from that of humans and dogs when a diagnostic tool called thromboelastometry is used to assess the status of blood flow and coagulation. Their work should improve clinicians’ ability to use thromboelastometry effectively in the care of critically ill horses.

The process by which the body halts bleeding and begins healing is called hemostasis. Through this complex process, the body essentially forms an organic Band-Aid. Factors such as disease, medications, and other conditions can affect hemostasis, which is why doctors in both human and veterinary medicine need ways to evaluate the status of this process in the patient.

In horses common diseases such as colic, colitis, endotoxemia, and sepsis are associated with alteration of the hemostatic pathway, leading to coagulation abnormalities in these horses. It is critical in these patients to have the ability to assess their current blood clotting situation for successful treatment.

Recently Maureen McMichael, DVM, MS, Dipl. ACVECC, and Pamela Wilkins, DVM, MS, PhD, Dipl. ACVIM, ACVECC, directed a study in order to further evaluate thromboelastometry for clinical use with horses. Stephanie Smith, DVM, MS, another faculty member at the University of Illinois College of Veterinary Medicine, and Tanya Rossi, DVM, a veterinary intern, also contributed to this study.

Thromboelastometry is a method that allows kinetic observation, in real time, of clots forming and dissolving.

“There has been very little if any standardization of how this test is conducted,” said McMichael.

Thromboelastometry is useful for looking at the interaction of coagulation factors, anticoagulant drugs, blood cells and platelets during clotting and fibrinolysis (the breakdown of clots). It uses conditions to mimic the flow of blood in veins in order to provide more precise results. There have not been dedicated parameters set for methodology and reference ranges in horses for this test.

In their study, McMichael and Wilkins determined how much of the clotting pathway occurs in citrated equine whole blood and what effects this has on results of the thromboelastometry. Citrate is a compound added to blood to prevent clotting from occurring since often the time between taking the blood sample and conducting the test is delayed. When the time comes to run the test, the blood is recalcified so that it can clot again and be tested. The effect of the holding time, which is how long the sample is actually kept before conducting the test, was also evaluated.

The team found that there were significant increases in the likelihood of the blood to coagulate as the holding period time was lengthened. They also found that there was a significant increase in pro-coagulant factor activity after a 30-minute holding time, and that there was a strong activation of the coagulation pathway during this time.

“Our study shows that horse blood is stimulated to clot much more quickly outside the blood vessels than is the blood of dogs or humans,” said Wilkins. "Horse blood has a very strong contact activation, which may partially explain why very sick horses are prone to clot quickly with some diseases."

Conclusively, with this research it was determined that in order to achieve the best results for thromboelastometry studies, a profound outside stimulation was needed when using recalcified blood. Without some sort of stimulation, the recalcified blood should not be used to study the system of hemostasis in horses.

“Our study showed that a strong trigger will help minimize the differences present in many cases,” said Wilkins.

McMichael added, "We believe we have set a standard to allow comparison across research institutions.”

The study, "Evaluation of contact activation of citrated equine whole blood during storage and effects of contact activation on results of recalcification-initiated thromboelastometry," was published in the American Journal of Veterinary Research.

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University of Illinois College of Veterinary Medicine

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