Erythropoietin (EPO)

The Erythropoietin (EPO) test, also known as epoetin or erythropoietin hormone level, supports diagnostic assessment of anemia and erythrocytosis by comparing circulating EPO with the degree of anemia or polycythemia. It helps distinguish anemia due to marrow suppression from anemia caused by insufficient endogenous EPO and is used to gauge renal EPO secretory capacity in chronic kidney disease. In patients with polycythemia, the test aids in identifying secondary causes driven by inappropriately elevated EPO. Results may also be used to anticipate and track clinical response to recombinant erythropoietin treatment for anemia.

Erythropoietin is released in response to tissue hypoxia and stimulates bone marrow to increase erythropoiesis. Adequate red blood cell production requires functional marrow, sufficient iron, vitamin B12, and folate stores, appropriate levels of erythropoietin, and marrow responsiveness to the hormone. Circulating erythropoietin activity is transient and falls as oxygen delivery improves; reduced renal synthesis or impaired marrow response can manifest as anemia. In contrast, excess erythropoietin production, including from renal or other tumors, can lead to secondary polycythemia with expansion of blood volume and increased viscosity. Erythropoietin demonstrates diurnal variation, and concentrations may be higher at high altitude.