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.
