Erythropoeitin

This test measures the amount of erythropoietin in the blood. Erythropoietin is a hormone produced mainly by the kidneys. It is produced and released into the bloodstream if the blood oxygen levels are low (hypoxaemia). Erythropoietin is carried to the bone marrow, where it works to stimulate stem cells to become red blood cells (RBCs). RBCs contain haemoglobin, 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 keep a stable number of RBCs. If there are too few produced or too many lost (through bleeding) or destroyed (haemolysis), or if the RBCs are abnormal (in shape, size or function of haemoglobin) then the patient will become anaemic and their ability to carry oxygen will be reduced. Normal red blood cell production relies on a functioning 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 how low the oxygen concentration is (hypoxia ) and the ability of the kidneys to produce erythropoietin. The hormone is active for a short period of time and is then removed 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 anaemic.

If there is too much erythropoietin produced, such as may occur with some benign or malignant kidney tumours 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.

In one type of polycythaemia, called polycythaemia rubra vera, the excessive production of red cells occurs independently of erythropoietin levels. In these patients the erythropoietin level may be quite low. In patients with other forms of excessive red blood cell production usually associated with lung disease the erythropoietin level is high.

How is the sample collected for testing?

A blood sample is collected by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.