Essential thrombocythaemia — Rapid | Doctor's Passport Education

Synopsis

Distinguish essential thrombocythaemia from reactive thrombocytosis and prefibrotic myelofibrosis, assess thrombosis and bleeding risk and use antiplatelet or cytoreductive treatment safely.

ET is a sustained platelet count at least 450 × 10⁹/L with characteristic marrow megakaryocytes, a clonal marker and exclusion of reactive thrombocytosis and other myeloid neoplasms.
First-line assessment is repeat FBC and film, ferritin and iron, CRP or ESR, renal and liver tests and review for infection, inflammation, bleeding, cancer, surgery and splenic status.
Test JAK2 V617F first, then CALR and MPL when negative; test BCR-ABL1 when features are atypical or no clear MPN driver is found.

Key red flags

Focal neurological deficit, chest pain, acute limb pain, abdominal splanchnic thrombosis or hypoxia requires immediate thrombosis assessment and treatment.

Major thrombosis

Stroke, coronary, DVT, PE and portal, hepatic or cerebral venous events can occur even with a modest platelet count.

Investigation priorities

First-line reactive-cause screenFirst stepFirst line

Confirm persistence and identify common non-clonal platelet drivers.

Management branches

Persistent platelets above 450Exclude reaction and classify marrow

Thrombocytosis persists on repeat FBC without an obvious transient cause.

Assess film, iron, inflammation, infection, bleeding, malignancy, surgery and spleen.
Test JAK2, then CALR and MPL, adding BCR-ABL1 when appropriate.

Key medicines

Low-dose aspirinGive 75 mg orally once daily when the thrombotic or microvascular indication outweighs bleeding risk; do not start during active bleeding or suspected acquired von Willebrand syndrome until assessed.

HydroxycarbamideStart commonly at 500 mg orally once or twice daily and titrate with frequent FBC to safe platelet and leukocyte control, adjusting the starting and maintenance dose for renal function, age and cytopenia.

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