Bleeding diatheses seen in clinical practice are usually divided into primary and secondary disorders. Several in-practice diagnostic tests are now available to help reach a specific diagnosis. Platelets can be counted by hematology equipment; however, the counts should always be validated by looking at a smear and estimating. Classic signs of thrombocytopenia include petechiation, ecchymosis, epistaxis, and gastrointestinal blood loss. Hemorrhage is not usually seen in patients unless the platelet count is less than 40,000 cells/mm3. Several standardized coagulation screening tests are useful to define coagulopathies in clinical practice. New point-of-care coagulation instruments (IDEXX Coag DX; www.idexx.com) use a small amount of blood to analyze the activated partial thromboplastin time and prothrombin time.
COMMENTARY: As indicated in this paper, the type of bleeding present often suggests the nature of the hemostatic defect. The concomitant presence of edema with surface hemorrhage suggests vasculitis. Mucosal hemorrhage, cutaneous bruising, and prolonged bleeding from surgical or traumatic wounds are typically seen in dogs with von Willebrand disease. However, in contrast to thrombocytopenia and inherited platelet function defects, petechiae do not appear to be a sign of von Willebrand disease in dogs. As stressed in this paper, the presence of platelet aggregates in blood samples often results in spuriously low measurement of platelet counts in automated hematology analyzers. Consequently, it is essential that blood films be examined to verify or refute the reported platelet count. The simultaneous evaluation of several hematology tests is generally required to adequately evaluate a bleeding patient. We typically get baseline information from the platelet count (or platelet estimate), activated partial thromboplastin time (or activated clotting time), and prothrombin time tests. If results of these tests are normal, then a bleeding time is indicated in an attempt to demonstrate that a platelet function abnormality or von Willebrand disease is present. Specialized tests are needed to differentiate these possibilities. If disseminated intravascular coagulation is suspected, fibrin degradation products or D-dimers tests are done to show the presence of concomitant fibrinolysis. If the antithrombin III assay is rapidly available, a low value provides evidence for coagulation factor activation in disseminated intravascular coagulation.-- John W. Harvey, DVM, PhD, Diplomate ACVP
A clinical approach to the bleeding patient. Giger U. NAVC PROC 2008, p 567.