The official WHO diagnostic criteria for PV allow bypassing bone marrow examination, for diagnostic purposes, in JAK2-mutated cases with Hb/Hct level above >18.5 g/dL/55.5% in men and 16.5 g/dL/49.5% in women, with subnormal serum Epo. The gene discussed is EPO; the disease is acquired polycythemia vera.