A low erythropoietin (EPO) level is a minor diagnostic criterion for polycythemia vera (PV). Controversies exist regarding the diagnostic value of a low EPO level when considering increasing availability of advanced molecular testing. We assessed the role of low EPO level for PV diagnosis in the context of positive JAK2 mutation status as well as other diagnostic parameters. Of 138 patients, 75 patients had PV and 63 had secondary erythrocytosis. Of the 75 patients with PV, 32% had EPO levels within the normal range. EPO level positively correlated with obesity and smoking status, making it an unreliable diagnostic marker in those patients. Although EPO level below normal as a standalone diagnostic modality was significantly associated with PV (odds ratio [OR] 0.857; p < 0.001), when JAK2V617F mutation status was included in the prediction model, the association of low EPO was not statistically significant (OR 0.962, p = 0.269). Positive JAK2V617F demonstrated a strong predictive value for PV (OR 670.5, p = 0.006) either alone or in combination with other variables. Results show that EPO level is not a reliable diagnostic marker due to physiologic variation in association with obesity and smoking.