Major diagnostic criteria for the diagnosis of PV include elevated haemoglobin concentration and/or haematocrit, accompanied by trilineage hyperplasia (panmyelosis), with pleomorphic mature megakaryocytes in the bone marrow, and NM_004972:JAK2 p.V617F or JAK2 exon 12 mutations. Here, JAK2 is linked to acquired polycythemia vera.