Platelets, or thrombocytes, are the cells circulating in the bloo that are involved in the cellular mechanisms of primary hemostasis leading to the formation of blood clots. In strict sense, the term platelet should be reserved for anucleated thrombocytes of mammals. Nucleated thrombocytes of nonmammalian vertebrates differ from the mammalian plates not only in having a nucleus and thus resembling B lymphocytes, but also these nucleated thrombocytes do not aggregate in response to ADP, serotonin and adrenaline (they do aggregate with thrombin, of course.) . Dysfunction or low levels of platelets predisposes to bleeding, while high levels, although usually asymptomatic, may increase the risk of thrombosis. An abnormality or disease of the platelets is called a thrombocytopathy which could be either a decrease in number ie thrombocytopenia, decrease in function ie thrombasthenia or an increase in number ie thrombocytosis.