Platelet aggregation is a major and common problem in blood samples from cats. This greatly affects the accuracy of counting of the platelets. Because of the difficulties in counting feline platelets, results for patients and reliable reference values for cat platelets are currently so inaccurate as to be almost useless in diagnosis of thrombocytopenia. In this study we used an effective method to prevent platelet aggregation. Blood was collected in CTAD test tubes and prostaglandin E1 was added to the blood sample.