Veterinary Clinical Medicine-I (General and Systemic)

Primary hemostasis: Platelets and vWF

PRIMARY HEMOSTASIS: PLATELETS & VWF 

• Since 8-15 platelets are normally found per high power oil emersion microscopic field, an absence to low number of platelets suggests a severe thrombocytopenia. Hemorrhage is generally not observed unless the platelet count is <40,000/µl (normal 150-500,000/µl). Detection of platelet-associated antibodies further supports an immune-mediated thrombocytopenia, but this test is rarely available. Serum titers or PCR tests for tick-born and other infectious diseases are indicated in certain countries or areas.
• The presence of schistocytes and thrombocytopenia suggests intravascular disseminated coagulation, where intravascular fibrin strands fragment erythrocytes. Because von Willebrand disease is such a common mild primary hemostatic defect in dogs, plasma vWF measurements by ELISA are indicated. Alternatively, DNA testing is available in some canine breeds for breeding purposes.
• Finally, in light of normal platelet count and plasma vWF values, a prolonged buccal mucosal bleeding time (BMBT) indicates a thrombopathia. Disposable devices are available that facilitate making 1-2 standard 1mm deep mucosal incisions. The platelet function analyzer (PFA100) is a simple tool to functionally assess primary hemostasis. Electron microscopic and platelet aggregation and nucleotide studies allow further characterization of platelet dysfunctions in specialized laboratories.