At a Glance
Why Get Tested?
Either to help differentiate between polycythaemia vera and secondary polycythaemia or to help differentiate between different types of anaemia and to determine whether the amount of erythropoietin being produced is appropriate for the level of anaemia present
When to Get Tested?
If a patient has an elevated red blood cell count or an anaemia that the doctor suspects may be caused by decreased red blood cell production
A blood sample drawn from a vein in your arm
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 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 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 maintain a relatively 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 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 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 (polycythaemia). 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 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 the erythropoietin level is high.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.