The most important aspect of diagnosis of hemostatic disorders is the collection and submission of an optimal sample for testing. Unlike many other clinical pathologic tests, coagulation assays are unforgiving with respect to poor sample collection and handling. Many causes of prolonged clotting times or decreased factor concentrations are artifactual, due to poor sample collection and handling.
Clean venipuncture is essential.
Poor venipuncture will result in activation of coagulation due to contamination with tissue factor. The sample should be mixed with anticoagulant rapidly to prevent clotting occurring within the tube. Therefore, vacutainer collection is preferred, although in some instances vacutainers can underfill. The hematocrit of the patient should be considered. The converse is true in anemic animals, in which a sample may clot due to undercitration.