To establish a diagnosis of PV, the 2008 WHO diagnostic criteria include the presence of erythrocytosis and the JAK2V617F or JAK2 exon 12 mutation (major criteria), as well as the presence of one minor criterion, such as bone marrow biopsy consistent with PV (hypercellularity and panmyelosis with prominent trilineage proliferation), low serum erythropoietin (EPO) level, or endogenous erythroid colony (EEC) formation in vitro. This evidence concerns the gene EPO and polycythemia.