A disease caused by essential thrombocytosis or other myelo-proliferative disorders such as chronic myelogenous leukaemia, polycythaemia, myelofibrosis. This disease can also have secondary causes such as inflammation, surgery, hyposplenism, splenectomy, asplenia, iron deficiency anaemia or haemorrhage. This disease is characterised by elevated platelet count in the blood. Confirmation is by identification of increased platelet count in a blood sample.