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 created and released into the bloodstream in response to low oxygen levels. Erythropoietin is carried to the bone marrow, where it works to stimulate
stem 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 there are too few produced or too many lost (through bleeding) or destroyed (hemolysis), or if the RBCs are abnormal (in shape, size, or function of hemoglobin), then the patient will become anemic and their ability to transport oxygen will diminish. 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 hypoxia and the ability of the kidneys to produce it. 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 patient’s bone marrow is unable to respond to the stimulation (such as may occur with a bone marrow disorder), then the patient may become increasingly anemic.
If there is too much erythropoietin produced, such as may occur 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 the blood in circulation, an increase in the blood’s viscosity, and to hypertension.
