Definition
Thrombocytosis is present, if the platelet count is elevated to over x 10⁹/L. A distinction is made between reactive and neoplastic (myeloproliferative) thrombocytosis.
  

Clinical picture:
Reactive thrombocytosis is rarely associated with platelets counts over 1,000 x 10⁹/L. If no additional risk factors for thromboembolism are present, reactive thrombocytosis does not normally lead to thrombosis. The highest values (over 3,000 x 10⁹/L) are observed in essential thrombocythemia (myeloproliferative disorder). This can be associated with an increase in bleeding and thrombotic complications.

Occurrence:

reactive	neoplastic
- Hemorrhage - Trauma - Post-operative - Chronic iron defeciency - Initially after splenectomy - Solid tumors - Chronic infections - Connective tissue diseases	In myeloproliferative syndromes, especially in essential thrombocythemia