Reactive<unk>  is the most common cause of a high platelet count. It accounts for 88% to 97% of<unk>  cases in adults, and near 100% in children. In adults, acute infection, tissue damage, chronic inflammation and malignancy are the common causes of reactive<unk> . Usually, one or more of these conditions is present in more than 75% of the cases with reactive<unk> . Causes for reactive<unk>  in children are similar to adults. In addition, hemolytic anemia and thalassemia are often present in children living in the Middle East. Other causes of reactive<unk>  include: post surgery, iron deficiency, drugs, and rebound effect after bone marrow suppression. The SARS disease caused thrombocytosis. Once the reactive causes of<unk>  are ruled out, clonal<unk>  should be considered. The most common cause of clonal<unk>  is a myeloproliferative neoplasm. These include: essential<unk> , chronic myelogenous leukemia, polycythemia vera, and primary myelofibrosis. Extremely rare causes of<unk>  are spurious causes. This is due to the presence of structures resembling platelets in the blood such as needle-like cryoglobulin crystals, cytoplasmic fragments of circulating leukemic cells, bacteria, and red blood cell microvesicles. These structures are counted as platelets by the automated machine counter; therefore, causing the platelet number to be falsely elevated. However, such error can be avoided by doing a peripheral blood smear.
Thrombocythemia
Leukostasis
Thrombocytopenia
Red cell agglutination
Leukocytosis
Lycopenemia
Reticulocytosis
Cytopenia