When you have anemia that your healthcare practitioner suspects may be caused by decreased red blood cell production; when you are producing too many red blood cells
A blood sample drawn from a vein in your arm
Erythropoietin (EPO) is a hormone produced primarily by the kidneys, with small amounts made by the liver. EPO plays a key role in the production of red blood cells (RBCs), which carry oxygen from the lungs to the rest of the body. This test measures the amount of erythropoietin in the blood.
The body uses a dynamic feedback system to help maintain sufficient oxygen levels and a relatively stable number of RBCs in the blood.
- Erythropoietin is produced and released into the blood by the kidneys in response to low blood oxygen levels (hypoxemia). The amount of erythropoietin released depends on how low the oxygen level is and the ability of the kidneys to produce erythropoietin.
- EPO is carried to the bone marrow, where it stimulates production of red blood cells. The hormone is active for a short period of time and then eliminated from the body in the urine.
- As oxygen levels in the blood rise to normal or near normal levels, the kidneys slow production of EPO.
However, if your kidneys are damaged and do not produce enough erythropoietin, then too few RBCs are produced and you can becomes anemic. Similarly, if your bone marrow is unable to respond to the stimulation from EPO, then you may become anemic. This can occur with some bone marrow disorders or with chronic diseases, such as rheumatoid arthritis. (Read Anemia of Chronic Diseases to learn more.)
If you have a condition that affects the amount of oxygen you breathe in, such as a lung disease, you may produce more EPO to try to compensate for the low oxygen level. People who live at high altitudes may also have higher levels of EPO and so do chronic tobacco smokers.
If you produce too much erythropoietin, which can happen with some benign or malignant kidney tumors and with a variety of other cancers, you may produce too many RBCs (polycythemia or erythrocytosis). This can lead to an increase in the blood's thickness (viscosity) and sometimes to high blood pressure (hypertension), blood clots (thrombosis), heart attack, or stroke. Rarely, polycythemia is caused by a bone marrow disorder called polycythemia vera, not by increased erythropoietin.
How is the test used?
An erythropoietin (EPO) test is used primarily to help diagnose the cause of anemia. An EPO test is usually ordered in follow up to abnormal results on a complete blood count (CBC), such as a low red blood cell (RBC) count and low hemoglobin and hematocrit. These tests help diagnose anemia and give the healthcare practitioner clues as to the likely cause of the anemia. Erythropoietin testing is used to help determine if low EPO may be causing and/or worsening the anemia.
If you have chronic kidney disease, an EPO test may be ordered to evaluate the kidneys' continued ability to produce enough erythropoietin. Testing can help determine whether you should receive erythropoietin replacement therapy. If the erythropoietin level is low, erythropoietin replacement therapy may help increase red cell production in the bone marrow.
Occasionally, an erythropoietin test may be ordered in follow up to CBC results that show an increased number of RBCs, to help diagnose the cause. Testing may help determine whether the excess production of RBCs (polycythemia or erythrocytosis) is due to an overproduction of erythropoietin or some other cause (e.g., JAK2 mutation, bone marrow disorder).
When is it ordered?
An erythropoietin (EPO) test may be ordered when you have anemia that does not appear to be caused by iron deficiency, vitamin B12 or folate deficiency, decreased lifespan of red blood cells (RBCs; hemolysis), or by excessive bleeding. It may be ordered when the RBC count, hemoglobin, and hematocrit are decreased and the reticulocyte count is inappropriately normal or decreased.
If you have chronic kidney disease, erythropoietin levels may be ordered when your healthcare practitioner suspects that kidney dysfunction could be associated with a decrease in erythropoietin production.
An EPO test may be ordered when a complete blood count shows that you have an increased number of RBCs and a high hematocrit and hemoglobin.
What does the test result mean?
If you have anemia and erythropoietin levels are low or normal, then your kidneys may not be producing enough EPO.
If you have anemia and erythropoietin levels are increased, then the anemia may be due to iron or vitamin deficiency, or a bone marrow disorder.
If you have too many red blood cells (RBCs) and erythropoietin levels are increased, then it is likely that excess erythropoietin is being produced – either by your kidneys or by other tissues in your body. This condition is called secondary polycythemia.
If you have too many RBCs and erythropoietin levels are normal or low, then it is likely that the polycythemia has a cause that is independent of erythropoietin production. This condition is called primary polycythemia.
Condition present EPO level Example(s) of possible cause(s) Anemia (low RBCs, hemoglobin and hematocrit) Low or normal Severe kidney disease, anemia of chronic disease Anemia High Bone marrow disorder (e.g., myelodysplastic syndrome) Polycythemia (high RBCs, hemoglobin and hematocrit) High EPO-producing kidney tumor or other tissue (secondary polycythemia) Polycythemia Normal or low Polycythemia vera (primary polycythemia)
Is there a treatment for low EPO?
A synthetic form of erythropoietin (recombinant human erythropoietin or rh-EPO) may be used as a treatment to help increase RBC production in people with chronic kidney disease and other anemias related to bone marrow suppression and/or failure, such as that due to radiation or chemotherapy treatment for cancer. The drug treatment, which is given through a vein (intravenously) or under the skin (subcutaneous injection), is expensive and its stimulation of the bone marrow lasts only a few hours. The synthetic hormone's use has been promising, helping to decrease the need for blood transfusions and improving the quality life for many affected people.
In June 2011, The U.S. Food and Drug Administration (FDA) recommended that healthcare professionals adjust the ESAs for more conservative dosing in patients with chronic kidney disease (CKD) to improve the safety of these drugs. The data indicated increased risks of cardiovascular events (e.g., heart attacks and strokes) with ESAs in this patient population.
Can adequate erythropoietin production by my kidneys be restored?
Not directly. If your low EPO is due to a temporary kidney condition, then it may resolve as the kidney condition resolves. In many cases, however, low EPO is due to chronic kidney disease and will not get better over time. Your healthcare practitioner will work with you to address and minimize the effects of the resulting anemia and may treat you with synthetic erythropoietin (i.e., erythropoietin replacement therapy).
Why isn't erythropoietin measured to monitor erythropoietin drug therapy?
It is not used because it is the effect on the bone marrow – reflected by increased RBC and reticulocyte production and increasing hemoglobin – that is important in the resolution of anemia, not the concentration of erythropoietin in the blood. The amount needed will vary from person to person depending on their condition and the responsiveness of their bone marrow.
I’ve heard some athletes are tested for EPO. Why?
Synthetic erythropoietin is also being used by some athletes as a form of "blood doping." Those who use it are trying to increase their endurance and oxygen capacity by increasing the number of RBCs in their blood. This use of the drug can be dangerous, resulting in hypertension and increasing the viscosity of the blood. Its use has been prohibited by most sports organizations, including the International Association of Athletics Federations, and erythropoietin is now being tested for as part of the Olympics anti-doping program. Read Drug Abuse Testing to learn more.
Is there anything else I should know?
If anemia is due to a vitamin B12, folate, or iron deficiency, then the anemia may persist even when enough erythropoietin is produced. The red blood cells (RBCs) produced in these deficiencies may not be normal in size, shape, and/or hemoglobin content.
Pregnant women, chronic smokers, and people with lung disease, or who live at high altitudes may have increased levels of erythropoietin.