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Erythropoietin (EPO)

A hormone made mostly by the kidneys that tells the bone marrow to make red blood cells. It is read alongside your hemoglobin.

AI-verified against cited sources. Awaiting expert reviewAlso called EPO, sEPOLOINC 15061-5

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What it is

Erythropoietin (EPO) is a hormone made mostly by the kidneys. When the kidneys sense low oxygen in the blood, they release more EPO. EPO tells the bone marrow to make more red blood cells. When red cell levels rise, EPO normally falls. Because of this, an EPO result only makes sense next to your hemoglobin or hematocrit.

Why it matters

Clinicians use EPO to help work out why a red blood cell count is too low (anemia) or too high (polycythemia). In anemia from causes like iron deficiency or red cells breaking down early, EPO is usually high, because the body is trying to make more cells. In polycythemia vera, a bone marrow condition, EPO is often low. An EPO value in the usual range can still be too low for a person with anemia, so it is never read alone.

If it’s low

A lower-than-usual EPO is not always a problem. It can also mean the kidneys are not making enough, as in chronic kidney disease, that long-term illness is dulling the response, or, when hemoglobin is high, that red cells are being made without EPO's signal, as in polycythemia vera. If you have anemia, an EPO inside the usual range can still be lower than expected.

Common causes

  • Chronic kidney disease
  • Anemia of chronic disease, such as long-term infection, rheumatoid arthritis or cancer
  • Polycythemia vera, a bone marrow condition that makes too many red cells
  • An underactive thyroid or poor nutrition

What can help

  • Ask your clinician how your EPO compares with what is expected for your hemoglobin
  • Ask whether your kidney function (creatinine and eGFR) should be checked
  • If your red cell count is high, ask whether further testing, such as a JAK2 mutation test, is worth discussing

If it’s high

A higher-than-usual EPO is common when the body is pushing to make more red blood cells, as in many anemias, or when oxygen levels are low. If your red cell count is also high, a high EPO can point to a cause outside the bone marrow, such as low oxygen or, rarely, a tumor that makes EPO. High EPO in someone with anemia is expected. High EPO together with a high hemoglobin needs a closer look.

Common causes

  • Anemia from iron deficiency, thalassemia, B12 or folate deficiency, or red cells breaking down early (the body is trying to make more cells)
  • Living at high altitude
  • Long-term low oxygen, for example from lung disease, sleep apnea or some heart conditions
  • Smoking
  • Receiving EPO as a medicine (the test cannot tell your own EPO from injected EPO)
  • Rarely, a tumor that makes EPO, such as some kidney, liver or uterine tumors

What can help

  • Ask your clinician to read your EPO together with your hemoglobin, hematocrit, ferritin and iron results
  • Ask whether low oxygen levels, for example from sleep apnea or lung disease, should be looked into
  • If you smoke, ask about support to quit, since smoking is linked to higher EPO and red cell counts

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on sex and age. Choose women or men to see the one that applies.

Children and teens 12 ranges

See EPO by age and sex, with the U.S. survey numbers where they exist.

What can affect your result

  • Hemoglobin and hematocrit: EPO normally rises as they fall and falls as they rise
  • Altitude: levels are higher at high altitude
  • Time of day: EPO varies through the day, so morning collection is advised
  • The assay brand, which changes both results and ranges
  • Smoking, lung disease and sleep apnea
  • Kidney function and long-term illness
  • Results from one brand of assay can differ a lot from another, so repeat tests should use the same lab and assay (Labcorp).
  • Antibodies such as HAMA (found in people regularly exposed to animals or who have had antibody-based treatments or scans) can interfere with antibody-based assays (Labcorp).
  • The test cannot tell your own EPO from EPO given as a medicine (Labcorp).
  • Living at high altitude raises EPO (Labcorp).
  • ARUP rejects hemolyzed samples, EDTA plasma and bone marrow aspirates.
  • In people being checked for a high red cell count, earlier blood removal (phlebotomy) and other health conditions can affect the result (Yoon 2024).

Quest recommends collecting between 7:30 am and noon because EPO varies through the day. For repeat tests, use the same time of day (Labcorp). EPO moves with oxygen supply and red cell count, and it also varies through the day.

When to talk to a clinician

An EPO result by itself is not urgent. Talk with your clinician about any EPO that does not fit your hemoglobin, especially if you also have ongoing tiredness, shortness of breath or paleness (low red cell counts), or a persistently high red cell count. If you have chest pain, trouble breathing, confusion, fainting, or sudden weakness or trouble speaking, call 911 or your local emergency number.

Questions you could ask

  • How should I read this result alongside my hemoglobin?
  • Should I repeat it at the same time of day and at the same lab?
  • Is my EPO higher than expected for my hemoglobin?
  • Could low oxygen, from altitude, sleep apnea, lung disease or smoking, explain this?
  • Is my EPO lower than expected for my hemoglobin?
  • Should we check my kidney function, or talk about further testing for a high red cell count?

Questions people ask

My EPO is in the usual range. Why is my clinician still asking about it?

EPO is judged against your hemoglobin. If you have anemia, EPO should rise well above the usual range, so a value inside the range can mean a weaker-than-expected response. If your red cell count is high, EPO should be low, so a value inside the range can also be worth a closer look.

Is mIU/mL the same as IU/L?

Yes. One mIU/mL equals one IU/L, so the number is the same in either unit. Some labs print mU/mL for the same thing.

Why do labs use different EPO ranges?

Different EPO tests give somewhat different numbers. For example, Labcorp and Quest print 2.6–18.5 mIU/mL for adults, while ARUP prints 4–27. Always compare your result with the range on your own report, and use the same lab for repeat tests.

Show the science and sources

Units

  • 1 mIU/mL = 1 mIU/mL
  • 1 mIU/mL = 1 IU/L

For clinicians and researchers

EPO is a glycoprotein of about 30.4 kDa produced mainly by the adult kidney (and fetal liver), with production driven by renal oxygen sensing; plasma levels vary inversely with hematocrit and are higher under hypoxia. It is measured by immunoassay (a chemiluminescent immunoassay at ARUP, an immunochemiluminometric assay at Labcorp), and results and reference limits depend on the assay: 2.6–18.5 mIU/mL (Labcorp, Quest adults, MedlinePlus), 4–27 mU/mL (ARUP), 4.3–29.0 IU/L (an assay maker's expected values, median 10.6) and 5.3–26.3 IU/L in a 393-donor study with no sex or age differences; published limits range from 2.2 to 34.0 IU/L. In uncomplicated anemia, EPO rises steeply as hematocrit falls (ARUP's expected-concentration graph spans 10 to 100,000 mU/mL on a log scale), so a value that is low for the degree of anemia, as seen with renal failure and anemia of chronic disease (Labcorp, MedlinePlus), is the finding of interest. Subnormal EPO supports polycythemia vera in the erythrocytosis work-up, but the cut-off is contested and EPO can be within normal limits in some patients with PV (Labcorp). In one single-center study of 41 patients with PV and 49 with secondary erythrocytosis, a cut-off of 3.1 IU/L had a sensitivity of 80.5% and specificity of 87.8%, while the lower reference limit of 5.3 IU/L had 97.6% and 65.3%. Elevated EPO is expected in secondary erythrocytosis from hypoxia (altitude, COPD, sleep apnea, cyanotic heart disease, smoking, high oxygen-affinity hemoglobin) and from EPO-producing tumors (renal cell carcinoma, hepatocellular carcinoma, uterine leiomyoma, cerebellar hemangioblastoma and others). In chemotherapy-treated cancer patients, a baseline EPO above 500 mIU/mL has been reported to predict no response to recombinant EPO (Labcorp). The assay cannot distinguish endogenous from recombinant EPO. Diurnal variation is documented (Quest advises collection between 7:30 am and noon). mIU/mL, mU/mL and IU/L are numerically identical.

LOINC 15061-5 (primary), 2237-6. Specimen: serum.

Sources

  1. Erythropoietin (test code 427), Dallas service area, Quest Diagnostics
  2. Erythropoietin (EPO) (test 140277), Labcorp
  3. Erythropoietin (test 0050227), ARUP Laboratories
  4. Erythropoietin test (Medical Encyclopedia), MedlinePlus, National Library of Medicine (2025)
  5. Diagnostic Performance of Serum Erythropoietin to Discriminate Polycythemia Vera from Secondary Erythrocytosis through Established 'Subnormal' Limits, Diagnostics (Basel) (2024)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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