Thrombocytosis
A platelet count over 450 x 10^9/L: telling reactive from clonal, iron deficiency and occult cancer as the usual reactive causes, when to send JAK2, CALR, MPL and BCR::ABL1, acquired von Willebrand syndrome above 1,000, and why reactive thrombocytosis doesn't need aspirin.
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Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Thrombocytosis is a platelet count over 450 x 10^9/L, the threshold in WHO 2022 criteria for essential thrombocythaemia (ET).
- Most is reactive. The usual culprits are infection, inflammation, iron deficiency, bleeding, recent surgery and cancer.
- The job is to find the reactive cause, or show there isn't one, before testing for a myeloproliferative neoplasm (MPN).
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Sources
- Investigation and management of thrombocytosis without JAK2, CALR or MPL mutations: A British Society for Haematology GuidelineGodfrey AL et al., Br J Haematol 2026;208:471-85, 2026 (online December 2025)
- Guideline for investigation and management of adults and children presenting with a thrombocytosisHarrison CN et al., Br J Haematol 2010;149:352-75, 2010
- The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Myeloid and Histiocytic/Dendritic NeoplasmsKhoury JD et al., Leukemia 2022;36:1703-19, 2022
- Philadelphia chromosome-negative classical myeloproliferative neoplasms: revised management recommendations from European LeukemiaNetBarbui T et al., Leukemia 2018;32:1057-69, 2018
- Clinical relevance of thrombocytosis in primary care: a prospective cohort study of cancer incidence using English electronic medical records and cancer registry dataBailey SER et al., Br J Gen Pract 2017;67:e405-13, 2017
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Personal emails, About story and Australian-style copy