The Test Sample
What is being tested?
This test measures the amount of erythropoietin in the blood. Erythropoietin is a hormone produced primarily by the kidneys. It is produced and released into the bloodstream in response to low blood oxygen levels (hypoxemia). Erythropoietin is carried to the bone marrow, where it works to stimulate precursor cells to become red blood cells (RBCs). RBCs contain hemoglobin, a protein that carries oxygen throughout the body. Normal RBCs have a lifespan of about 120 days and are usually similar in size and shape.
The body has a dynamic feedback system that attempts to maintain a relatively stable number of RBCs. If too few are produced or too many lost through bleeding or destruction (hemolysis) due to abnormal shape, size, function, or other causes, then the affected person becomes anemic and their ability to transport oxygen diminishes. Normal red blood cell production relies on the functional ability of the bone marrow, on an adequate supply of iron and nutrients such as vitamin B12 and folate, and on an appropriate concentration of and response to erythropoietin.
The amount of erythropoietin released depends upon the severity of the hypoxemia and the ability of the kidneys to produce erythropoietin. The hormone is active for a short period of time and then eliminated from the body in the urine. Increased production and release of erythropoietin continues to occur until oxygen levels in the blood rise to normal or near normal concentrations, then production falls. However, if the kidneys are damaged and/or unable to keep up with the demand for erythropoietin, or if the bone marrow is unable to respond to the stimulation, such as may occur with a bone marrow disorder, then the person typically becomes anemic.
If there is too much erythropoietin produced, as occurs with some benign or malignant kidney tumors and with a variety of other cancers, too many RBCs may be produced (polycythemia). This can lead to an increase in the volume of red cell mass in circulation, an increase in the blood’s viscosity, and sometimes to hypertension, thrombosis, heart attack, or stroke. Rarely, polycythemia is caused by a bone marrow disorder, not by increased erythropoietin.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.