The erythropoietin test measures the amount of a hormone called erythropoietin ((EPO) in blood.

The hormone acts on stem cells in the bone marrow to increase the production of red blood cells. It is made by cells in the kidney, which release the hormone when oxygen levels are low.

See also: Reticulocyte count

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

No special preparation is necessary.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

This test may be used to help determine the cause of anemia, polycythemia (high red blood cells) or other bone marrow disorders.

A change in red blood cells will affect the release of EPO. For example, persons with anemia have too few red blood cells, so more EPO is produced.

The normal range is 0-19 milliunits per milliliter (mU/mL).

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

Increased EPO levels may be due to secondary polycythemia, an overproduction of red blood cells that occurs in response to an event such as low blood oxygen levels. This may happen at high altitudes or, rarely, because of a tumor that releases EPO.

Lower-than-normal EPO levels may be seen in chronic kidney failure, anemia of chronic disease, or polycythemia vera.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)