Table 1.

2016 World Health Organization diagnostic criteria for polycythemia vera and essential thrombocythemia

	Polycythemia vera (PV) a	Essential thrombocythemia (ET) b
Major criteria
1	Hemoglobin > 16.5 g/dL(men) Hemoglobin > 16.0 g/dL (women) or Hematocrit > 49% (men) Hematocrit > 48% (women) or increased red cell mass (RCM)c	Platelet count ≥ 450 × 109/L
2	BM biopsy showing hypercellularity for age with trilineage growth (panmyelosis) including prominent erythroid, granulocytic and megakaryocytic proliferation with pleomorphic, mature megakaryocytes (differences in size)	BM biopsy showing proliferation mainly of the megakaryocyte lineage with increased numbers of enlarged, mature megakaryocytes with hyperlobulated nuclei. No significant left-shift of neutrophil granulopoiesis or erythropoiesis and very rarely minor (grade 1) increase in reticulin fibersd
3	Presence of JAK2 or JAK2 exon 12 mutation	Not meeting WHO criteria for BCR-ABL1 + CML, PV, PMF, MDS, or other myeloid neoplasms
4		Presence of JAK2, CALR or MPL mutation
Minor criteria
1	Subnormal serum erythropoietin level	Presence of a clonal marker (e.g., abnormal karyotype) or absence of evidence for reactive thrombocytosis

Table adapted from Barbui T et al. Blood Cancer J 2015; 5:e337¹⁰³ and Arber et al. Blood 2016;127:2391–2405²

BM, bone marrow; CML, chronic myeloid leukemia; MDS, myelodysplastic syndrome

^aPV diagnosis requires meeting either all three major criteria or the first two major criteria and one minor criterion

^bET diagnosis requires meeting all four major criteria or first three major criteria and one minor criterion

^cMore than 25% above mean normal predicted value

^dGrading of BM fibers⁸⁷

Criterion number 2 (BM biopsy) may not be required in cases with sustained absolute erythrocytosis: hemoglobin levels. 18.5 g/dL in men (hematocrit, 55.5%) or 16.5 g/dL in women (hematocrit, 49.5%) if major criterion 3 and the minor criterion are present. However, initial myelofibrosis (present in up to 20% of patients) can only be detected by performing a BM biopsy; this finding may predict a more rapid progression to overt myelofibrosis (post-PV MF)