Table 2.

Diagnostic criteria for ET (WHO vs PVSG)

Criteria
WHO-ET16	PVSG-ET14
Sustained platelet count > 450 × 109/l	Platelet count > 600 × 109/l
Bone marrow biopsy specimen showing proliferation mainly of the megakaryocytic mass lineage with increased numbers of enlarged mature megakaryocytes	Hematocrit < 40% or normal RBC
No sign of increase or left shift of neutrophil granulopoiesis or erythropoiesis	No myelodysplastic syndrome
Not meeting WHO criteria for PV; PMF, CML, MDS, or other myeloid neoplasms	No Philadelphia chromosome
Demonstration of JAK2V617F or other clonal marker, or in absence of clonal marker	No reactive cause
No evidence of reactive thrombocytosis	Collagen fibrosis absent or < one-third biopsy area without marked splenomegaly and leukoerythroblastic reaction

CML, chronic myeloid leukemia; MDS, myelodysplastic syndrome.