Erythropoietin (EPO) is a glycoprotein hormone of key importance for haematopoiesis, especially erythropoiesis – the production and maturation of erythrocytes. It is synthesised mainly by the interstitial cells of the renal cortex and, to a lesser extent, by hepatocytes. EPO production is regulated by feedback mechanisms in response to reduced blood oxygen saturation (hypoxia), blood loss or the onset of anaemia.
The role of EPO in physiology and pathophysiology
The primary stimulus for hormone secretion is hypoxia — a state in which oxygen transport in the body is insufficient, leading to increased expression of the EPO gene through activation of the HIF-1α factor. The hormone acts on bone marrow precursor cells, intensifying the proliferation and differentiation of erythroblasts, and indirectly also affects other haematopoietic lineages, including platelets.
Indications for measuring erythropoietin concentration
Testing EPO levels is an important tool in the diagnosis of various types of anaemia (both deficiency and aplastic) and polycythaemia. It is ordered in order to:
- differentiate the causes of haematological disorders,
- assess kidney function,
- monitor therapy in chronic diseases, haematological malignancies and bone marrow disorders,
- control the treatment of anaemia, especially when recombinant erythropoietin is used,
- in sports medicine – detect the illicit use of doping agents.
Test procedure
EPO is usually measured in a venous blood sample taken from the antecubital vein. The procedure is safe and requires no special preparation. It is recommended, however, that the patient fasts for 8–12 hours before sampling and avoids intense physical activity. Because of the circadian rhythm of hormone secretion (maximum values at night, minimum in the afternoon), the optimal sampling time is in the morning.
EPO reference ranges
In healthy individuals, plasma erythropoietin concentration usually falls within the range of 4.3–29 IU/L, although reference values may differ between laboratories. The hormone level depends on age, sex, physiological state (e.g. pregnancy) and the patient’s current health condition.
Interpretation of results
Elevated EPO concentration is observed, among others, in:
- iron deficiency,
- haemolytic anaemias,
- suppression of erythropoiesis in the bone marrow,
- cancers of the kidney and liver, Wilms tumour,
- chronic heart or lung diseases,
- tobacco smokers,
- conditions of increased oxygen demand – e.g. pregnancy, training under altitude hypoxia.
Reduced EPO concentration may indicate:
- anaemia due to renal failure,
- autoimmune diseases (rheumatoid arthritis, systemic lupus erythematosus),
- myeloproliferative diseases of the bone marrow (e.g. polycythaemia vera),
- advanced uraemia.