• There are many etiologies for changes in platelet number and bleeding can occur when there are either too many or too few platelets.

  • In essential thrombocythemia (ET) the JAK2617V kinase mutation is found in approximately 50% of patients, and if present is diagnostic.

  • The normal platelet count is considered to be 145-450x109/L (150,000 to 450,000 / ul), although this range varies among laboratories.

  • Thrombocytosis can be primary, i.e. as part of one of the myeloproliferative disorders, or secondary, usually as a reaction to neoplasms or infection.

  • The results of the remainder of the FBC often provide the most important additional information.

  • Symptoms rarely occur unless platelet counts are greater than 600x109/L (600,000 / ul).

  • When the platelet count is increased above normal, patients may experience either bleeding or thrombotic complications.
      (a) This is uncommon until platelet counts are in excess of1000x109/L

      (b) Symptoms are more common when thrombocytosis is primary rather than secondary (Schafer,2004).

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