The major criteria are a platelet count greater than 450 K/μL, bone marrow biopsy showing a proliferation of hyperlobated megakaryocytes with infrequent clusters and no significant fibrosis or left shift, criteria for other neoplasms must not be met (CML, PV, PMF, or other myeloid neoplasms), and presence of the JAK2, CALR, or MPL mutation. This evidence concerns the gene MPL and acquired polycythemia vera.