Tefferi et al listed revised criteria for the diagnosis of essential thrombocythemia (ET). These incorporate new developments associated with the JAK2 gene. The authors are from an ad hoc international expert panel for the World Health Organization (WHO).



(1) sustained platelet count >= 450,000 per µL (elevated)

(2) proliferation of large, mature megakaryocytes in a bone marrow biopsy without a significant increase in cells from the granulocytic or erythyroid series

(3) one or both of the following:

(3a) presence of JAK2 mutation (JAK2 617V>F, other)

(3b) exclusion of reactive thrombocytosis

(4) exclusion of other myeloproliferative, myelodysplastic or bone marrow disorders



• Causes of reactive thrombocytosis include inflammation, chronic infection, iron deficiency, surgery, metastatic cancer, autoimmune disorder, lymphoproliferative disorder, and post-splenectomy.


The diagnosis of ET requires the presence of all 4 criteria.


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