Thrombocytosis

• Thrombocytosis is defined as a platelet count greater than 450 × 109/L.
• Primary causes of thrombocytosis:

  ·       Polycythaemia rubra vera.

  ·       Chronic myeloid leukaemia.

  ·       Essential thrombocythaemia.

  ·       Primary myelofibrosis.

  ·       Unspecified myeloproliferative disorders.

  Caused by an abnormality in bone marrow function that arises from an expansion of a mutated haematopoietic stem cell or myeloid progenitor cells that give rise to megakaryocytes.
• Secondary causes of thrombocytosis:

  ·       Chronic inflammation (for example, rheumatoid arthritis or systemic lupus erythematosus).

  ·       Drug therapy (for example, corticosteroids).

  ·       Haemolysis.

  ·       Iron deficiency — this is the most common cause of secondary thrombocytosis.

  ·       Severe systemic infections (such as pericarditis or endocarditis).

  ·       Some specific cancers - Cancer cells trigger the coagulation cascade.

  ·       Splenectomy, hyposplenism.

  ·       Surgery, bleeding, and other trauma.
• Where no underlying cause is identified, and the person remains asymptomatic — repeat the full blood count in 4–6 weeks.

  • For people with suspected cancer — refer using a suspected cancer pathway referral (for an appointment within 2 weeks).