Erythropoietin (EPO, The EPO Test)

Measuring blood levels of erythripoietin, a hormone involved in red blood cell production, can diagnose some medical conditions.

• Erythropoietin (EPO) is a hormone produced by the kidney.
• Erythropoietin promotes the formation of red blood cells by the bone marrow.
• The erythropoietin hormone level can be detected and measured in the blood (the EPO test).
• Measurement of the blood erythropoietin level can be used to detect certain medical conditions.
• Erythropoietin can be synthesized and used as a treatment of some forms of anemia.
• Erythropoietin has been misused as a performance-enhancing drug by some athletes.

Erythropoietin (EPO) is a hormone produced by the kidney that promotes the formation of red blood cells by the bone marrow.

The kidney cells that make erythropoietin are sensitive to low oxygen levels in the blood that travels through the kidney. These cells make and release erythropoietin when the oxygen level is too low. A low oxygen level may indicate a diminished number of red blood cells (anemia), or hemoglobin molecules that carry oxygen through the body.

Erythropoietin stimulates the bone marrow to produce more red blood cells. The resulting rise in red cells increases the oxygen-carrying capacity of the blood.

As the prime regulator of red cell production, erythropoietin's major functions are to:

1. Promote the development of red blood cells.
2. Initiate the synthesis of hemoglobin, the molecule within red blood cells that transports oxygen.

Chemically, erythropoietin a protein with an attached sugar (a glycoprotein). It is one of a number of similar glycoproteins that serve as stimulants for the growth of specific types of blood cells in the bone marrow.

Erythropoietin is produced to a lesser extent by the liver. Only about 10% of erythropoietin is produced in the liver. The erythropoietin gene has been found on human chromosome 7 (in band 7q21). Different DNA sequences flanking the erythropoietin gene act to control liver versus kidney production of erythropoietin.

The erythropoietin hormone can be detected and measured in the blood. An abnormal level of erythropoietin in the blood can indicate bone marrow disorders, (such as polycythemia, or increased red blood cell production) kidney disease, or erythropoietin abuse. Testing erythropoietin blood levels is of value if:

• Too little erythropoietin might be responsible for too few red blood cells (anemia), especially anemia related to kidney disease.
• Too much erythropoietin might be causing too many red blood cells (polycythemia).
• Too much erythropoietin might be evidence for a kidney tumor.
• Too much erythropoietin in an athlete may suggest erythropoietin abuse.

The patient is usually asked to fast for 8-10 hours (overnight) and sometimes to lie quietly and relax for 20 or 30 minutes before the test. The test requires a routine sample of blood, which is sent to the laboratory for analysis.

Normal levels of erythropoietin range from 4 up to 24 mU/ml (milliunits per milliliter).

Abnormal erythropoietin levels suggest possible disease of the bone marrow or kidneys. Another possibility is abuse by an athlete to increase the red cell count for better athletic performance. The correct interpretation of an abnormal erythropoietin level depends on the particular clinical situation. Sometimes, the erythropoetin level may be inappropriately normal when it should be elevated (such as when there is an anemia), indicating a problem with the kidneys.

Yes. For example, erythropoietin has been misused as a performance-enhancing drug in athletes such as cyclists (in the Tour de France), long-distance runners, speed skaters, and Nordic (cross-country) skiers. When misused in such situations, erythropoietin is thought to be especially dangerous (perhaps because dehydration due to vigorous exercise can further increase the thickness (viscosity) of the blood, raising the risk for blood clots, heart attacks, and strokes. Erythropoietin has been banned by the Tour de France, the Olympics, and other sports organizations.

Yes. Using recombinant DNA technology, erythropoietin has been synthetically produced for use as a treatment for persons with certain types of anemia. Erythropoietin can be used to correct anemia by stimulating red blood cell production in the bone marrow in these conditions. The medication is known as epoetin alfa (Epogen, Procrit) or as darbepoietin alfa (Arnesp). It can be given as an injection intravenously (into a vein) or subcutaneously (under the skin).

Erythropoietin is used in many clinical settings. The most common use is in people with anemia (low blood count) related to kidney dysfunction. When the kidneys are not properly functioning, they produce less than normal amounts of erythropoietin, which can lead to low red blood cell production, or anemia. Therefore, by replacing the erythropoietin with an injection of synthetic erythropoietin, anemia related to kidney disease may be treated. Currently, Epogen or Procrit is a standard part of therapy in patients with kidney disease who require dialysis to both treat and prevent anemia.

Other uses of erythropoietin may include treatment of anemia related to the medication AZT (used to treat AIDS), anemia caused by chemotherapy, anemia caused by dysfunctional bone marrow (where the blood cells are made), and anemia associated with cancer.