Overall, there is a body of evidence from veterinary and human medicine that strongly suggests that TEG or ROTEM assays using citrated samples that employ an activator have significantly lower inherent variability than those that use recalcification alone. There is also strong evidence in dogs, cats, and humans that the results obtained using different activators are not directly comparable. There is no evidence to suggest that any one activating agent is superior to another for all patient populations, or drug monitoring indications. As such, use of more than one assay for complete thromboelastographic evaluation of a patient's coagulation system may be warranted. Standardization of the concentrations of activators would be beneficial.