Causes of reactive (secondary) The causes of reactive (secondary) are described below. Inflammatory disorders These conditions may cause by similar mechanisms to infections. Kawasaki's disease is a rare condition, mainly affecting children, in which there is widespread inflammation of the arteries. It is characteristically associated with a high platelet count that gradually resolves in the recovery phase. In adults either a high or low platelet count may accompany other features of 'autoimmune' diseases such as rheumatoid arthritis. Acute and chronic blood loss The response of the bone marrow to blood loss is to produce not only more red blood cells but also more - this occurs in response to cytokines. Tissue damage from trauma or surgery The count will also increase when a relatively large amount of body tissue is damaged either intentionally following surgery or with accidental damage. This is part of the natural defence mechanism to ensure adequate clot formation and prevent fatal bleeding. Medicines Rarely treatment with some drugs (steroid, vincristine) causes a transient increase in platelet count. These drugs are sometimes used to treat patients with a low platelet count due to (ITP). Underactive or absent spleen The spleen is one of the major sites for destroying platelets and if it is removed the count usually increases. The increase may remain for a long time but usually it settles back into the normal range. In some conditions the spleen is present but either it does not function properly (for example in some patients with Coeliac disease) or it is shrunken (for example in sickle cell disease) and the platelet count is sometimes elevated in these conditions. In this case examination of blood cells under a microscope may reveal characteristic changes suggesting impaired function of the spleen. Malignancy Some cancers can cause a count either by causing damage to tissues, causing blood loss (for example from the bowel) or by erroneously producing a cytokine that stimulates the bone marrow to produce platelets. Rebound from chemotherapy Some chemotherapy drugs exert their effects directly on dividing cells in the body - including the bone marrow where platelets are made. When the body is recovering from the effects of such a transient overproduction of some cells can occur. Causes of associated with bone marrow disorders The causes of associated with bone marrow disorders are described below. Essential , polycythaemia vera and myelofibrosis These three conditions form a group of diseases known as the myeloproliferative disorders (MPDs). An elevated platelet count can occur in all of them but in each an increase in a particular cell type predominates. These are the platelets in essential (ET), red cells in polycythaemia vera (PV) and fibroblasts (cells which manufacture fibrous tissue) in myelofibrosis (MF). Chronic myeloid leukaemia was in the past grouped with the MPDs but is now classified independently as its course is very different, and it has a distinct biology. Myelodysplastic syndromes This is a group of conditions in which the bone marrow manufactures blood cells inefficiently. Usually the platelet count is low in but in certain subtypes of this disease it may be higher. Sometimes it can be difficult to distinguish between this condition and a MPD and sometimes patients are classified as having an overlap syndrome. | 
