The proportion of patients with EPO levels below the normal range was significantly (p < 0.05) higher in NNE patients with bone marrow examination (18 out of 44) than in patients who were suspected of having NNE without bone marrow examination (30 out of 131) based on Hb above the diagnostic criteria for PV and JAK2 V617F mutation negativity. Here, EPO is linked to acquired polycythemia vera.