Erythropoietin

An erythropoietin (EPO) test is used primarily to help diagnose the cause of anemia. It can help identify candidates for erythropoietin replacement therapy (e.g., people with chronic kidney disease). Sometimes it is used to help diagnose the cause of too many red blood cells (polycythemia or erythrocytosis) or as part of an evaluation of a bone marrow disorder.

An EPO test is usually ordered in follow up to abnormal findings on a complete blood count (CBC), such as a low red blood cell (RBC) count and low hemoglobin and hematocrit. These tests establish the presence and severity of anemia and give the healthcare practitioner clues as to the likely cause of the anemia. Erythropoietin testing is ordered to help determine if low EPO may be causing and/or worsening the anemia.

In people with chronic kidney disease, the test may be ordered to evaluate the kidneys' continued ability to produce sufficient erythropoietin. 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 determine whether the excess production of RBCs (polycythemia or erythrocytosis) is due to an overproduction of erythropoietin or some other cause (e.g.,mutationJAK2).

An erythropoietin (EPO) test may be ordered when a person has 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 someone has chronic kidney disease, erythropoietin levels may be ordered when the 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 reveals that a person has an increased number of RBCs and a high hematocrit and hemoglobin.

An EPO test may be ordered when a healthcare practitioner suspects that a person has a bone marrow disorder, such as a myeloproliferative neoplasms (MPNs) or myelodysplastic syndrome (MDS).

If a person is anemic and erythropoietin levels are low or normal, then the kidneys may not be producing an appropriate amount of the hormone.

If a person is anemic and erythropoietin levels are increased, then the anemia may be due to iron or vitamin deficiency, or a bone marrow disorder.

If a person has too many red blood cells (RBCs) and erythropoietin levels are increased, then it is likely that excess erythropoietin is being produced – either by the kidneys or by other tissues in the body. This condition is called secondary polycythemia.

If there is excess RBC production 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.

If anemia is due to a vitamin B12, folate, or iron deficiency, then the anemia may persist even when adequate amounts of erythropoietin are being produced. The red blood cells (RBCs) produced in these deficiencies may not be normal in size, shape, and/or hemoglobin content.

If someone is producing an abnormal form of hemoglobin, such as may occur with thalassemia, or has a bone marrow disorder, then erythropoietin replacement therapy will not help resolve the anemia.

Those who are pregnant, who are chronic smokers, have lung disease, or who live at high altitudes may have increased levels of erythropoietin.

A synthetic form of erythropoietin (recombinant human erythropoietin or rh-EPO) has been developed 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 intravenously or by 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 March 2007, however, the U.S. Food and Drug Administration (FDA) issued stronger safety warnings with regard to erythropoiesis-stimulating agents (ESAs). The public health advisory included revised product labeling and recommendations to monitor the health of those on ESAs, especially people with cancer or kidney disease. The safety information recommends that healthcare practitioners monitor red cell levels (hemoglobin levels) and prescribe only the amount of ESA needed to stimulate the production of red cells to avoid blood transfusions. If some people are given higher than recommended doses, they run an increased risk of developing blood clots, heart attacks, strokes, and death. Also, certain people with cancer may experience a growth in tumor size.

The same 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.