JAK2 and acquired polycythemia vera: The 2016 WHO diagnostic criteria for PV include three major criteria and one minor criterion: hemoglobin > 16.5 g/dL and > 16.0 g/dL in men and women, respectively, or hematocrit > 49% (men)/> 48% (women), or an increased red cell mass; bone marrow biopsy showing hypercellularity for age with trilineage growth (panmyelosis) including prominent erythroid, granulocytic, and megakaryocytic proliferation with pleomorphic, mature megakaryocytes (differences in size); and the presence of JAK2 or JAK2 exon 12 mutation.