Not meeting WHO criteria for BCR-ABL1+ CML, PV, PMF, myelodysplastic syndromes, or other myeloid neoplasms Presence of JAK2, CALR, or MPL mutation Minor criterion Presence of a clonal marker or absence of evidence for reactive thrombocytosis Diagnosis of ET requires meeting all 4 major criteria or the first 3 major criteria and the minor criterion