Thrombocytosis or thrombocythaemia is the presence of abnormally high platelet count counts. Etiology can either be primary (essential) often due to a myeloproliferative disease (essential thrombocytosis, CML, myelofibrosis and polycythaemia vera) or reactive (due to a secondary cause like inflammation, surgery, haemorrhage, splenectomy, asplenia and hyposlenism).