World Health Organization requires 4 major criteria or first three major criteria + 1 minor criterion.
Major:
Sustained platelet count > 450 × 109/L Bone marrow biopsy with characteristic changes Not meeting WHO criteria for BCR-ABL+ CML, PV, PMF, myelodysplastic syndromes, or other myeloid neoplasm Presence of JAK2, CALR, or MPL mutation
Minor: presence of clonal marker or absence of evidence for secondary thrombocytosis
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