erythropoietin
Meaning of erythropoietin: The kidney doubles as an oxygen meter, releasing this hormone whenever the blood passing through it carries less oxygen than it should.
Definition of erythropoietin
Erythropoietin is a hormone made mainly in the kidneys that tells the bone marrow to produce more red blood cells. Cells within the kidney sense how much oxygen the blood reaching them carries, and release more of the hormone when that level falls. Laboratory made versions are given as medicines, and the hormone is often shortened to EPO.
How does the kidney know to release it?
Specialized cells sitting between the kidney tubules act as the sensor. When oxygen delivery to them drops, a regulating protein that is normally destroyed within minutes survives instead, builds up, and switches on the erythropoietin gene. Levels can climb steeply within hours. The hormone travels in the blood to the bone marrow, where it keeps immature red cell precursors alive long enough to mature rather than dying off, and that is how the marrow raises output. New red cells appear in the circulation within days, and the rise in oxygen carrying capacity switches the signal back off. Living at altitude, chronic lung disease, heavy smoking and a few tumors all drive the same loop. A small amount of the hormone is also made in the liver, enough to matter before birth but not enough to compensate for failing kidneys later in life.
Why does kidney disease cause anemia?
Damaged kidneys make less erythropoietin even though the marrow remains able to respond. The result is an anemia out of proportion to anything else, with normal sized red cells and no shortage of iron to explain it. This is the reverse of the usual pattern, in which anemia from any other cause drives erythropoietin levels up. That contrast is useful in the laboratory: a high red cell count with a low hormone level suggests the marrow is producing independently of the signal, while a high red cell count alongside a high hormone level points instead to a source of excess hormone or to a low oxygen state.
What are the manufactured versions used for?
| Setting | Why the hormone is given |
|---|---|
| Anemia of chronic kidney disease | Replaces the hormone the kidneys no longer make |
| Anemia during some cancer treatments | Supports red cell production suppressed by chemotherapy |
| Before certain planned surgery | Raises the red cell count ahead of expected blood loss |
These drugs are given by injection and include short acting forms and longer acting ones such as methoxypolyethylene glycol epoetin beta. They correct a count slowly rather than immediately, and iron has to be available for the marrow to use. Pushing the red cell count to or above a normal level has been linked with more clots and strokes and, in some cancer settings, with worse outcomes, so treatment targets sit deliberately below a normal hemoglobin. The same drugs are prohibited in competitive sport, where they were used to raise endurance.
Also known as
Used in a sentence
Erythropoietin levels were checked as part of the evaluation for the patient's chronic anemia.
Good to know
Anemia caused by low erythropoietin production, as seen in chronic kidney disease, is distinguished from anemia caused by iron deficiency or blood loss, since the underlying cause determines whether replacing the hormone itself is an appropriate treatment.
Word origin
Where “erythropoietin” comes from
Formed from Greek erythros, meaning red, and -poietin, from poiein, meaning to make.