According to the WHO guidelines, the diagnosis is now based on three major criteria: elevated Hb (> 16.5 g/dL in men and > 16 g/dL in women) or Htc levels (> 49% in men and > 48% in women) or increased RBC mass (> 25% above mean normal predicted value); bone marrow biopsy (BMB) with features of PV (hypercellularity for age, panmyelosis, and prominent erythroid growth); the presence of Janus kinase 2 (JAK2) V617F mutation (exon 14) or JAK2 exon 12 mutation (which together accounts for 98% of cases) [4,5]. The gene discussed is JAK2; the disease is acquired polycythemia vera.