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Blood Test Tracker

Nucleated Red Blood Cells (nRBC) (Percent)

How many nucleated red blood cells are in the blood for every 100 white blood cells. Healthy people usually have none after the first weeks of life.

AI-verified against cited sources. Awaiting expert reviewAlso called NRBC, nRBC, NRBC%LOINC 58413-6

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What it is

Red blood cells start out in the bone marrow with a nucleus, the cell's control center, and push it out before they enter the bloodstream. Nucleated red blood cells (nRBCs) are young red cells that still have their nucleus. They are normal in the blood of a fetus and a newborn, but they are rarely seen in healthy people after the first weeks of life. Labs report them per 100 white blood cells, so a result of 2 means 2 nRBCs for every 100 white cells counted.

Why it matters

Finding nRBCs in the blood of an older child or adult is unusual. It can mean the bone marrow is under stress and releasing young red cells early, for example after significant blood loss, when oxygen levels are low, or when red blood cells are breaking down faster than normal. It can also be linked to bone marrow conditions and to being very sick in hospital. Analyzers can mistake nRBCs for white blood cells, so labs often correct the white count when nRBCs are present. In newborns, a few nRBCs are expected.

If it’s high

Any nRBCs in an adult's blood are more than expected. A very small number is sometimes seen in healthy adults. Your clinician will usually look into it, because the reasons range from treatable ones, like blood loss, to bone marrow conditions. The answer usually comes from your hemoglobin, your reticulocyte count and a look at your blood smear.

Common causes

  • A very small number is occasionally seen in healthy adults, for example blood donors
  • Being a newborn, when nRBCs are normal and usually gone within the first weeks
  • Significant blood loss or low oxygen levels
  • Red blood cells breaking down faster than usual (hemolytic anemia), including conditions such as sickle cell disease and thalassemia
  • Being seriously ill, for example with sepsis or other critical illness
  • Bone marrow conditions, such as chronic myeloid leukemia or myelodysplastic syndromes

What can help

  • Ask your clinician to look at your nRBC result together with your hemoglobin, reticulocyte count and a blood smear
  • Ask whether the test should be repeated to see whether nRBCs are still there
  • Tell your clinician about any recent bleeding, surgery, illness or time in hospital

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 age. Choose an age to see the one that applies.

Children and teens 1 ranges

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

What can affect your result

  • Age: nRBCs are expected in newborns and normally clear within the first weeks of life
  • Blood loss, low oxygen levels and red blood cells breaking down faster than normal
  • Critical illness
  • The lab's method: analyzers count nRBCs automatically, and some labs also check by microscope
  • Units: results are per 100 white blood cells, even when shown with a % sign
  • Many analyzers count nRBCs as white blood cells, which makes the first white blood cell count read too high. Labs usually correct the white count when nRBCs are found.
  • Labs differ in how they count nRBCs (automated counter, or by microscope) and in the level at which they correct the white blood cell count.
  • Bleeding, low oxygen levels, red blood cells breaking down and serious illness can all release nRBCs, so recent illness can change a result.

Can change from one test to the next as the underlying cause comes and goes.

When to talk to a clinician

In an adult, any nRBC result is worth discussing with your clinician at your next visit. Contact your clinician promptly if you also feel very tired or short of breath, look pale or yellow, or have signs of bleeding. Call 911 or your local emergency number for chest pain, fainting, confusion or severe trouble breathing. A newborn's result is interpreted by the baby's care team.

Questions you could ask

  • Did my lab correct my white blood cell count for nRBCs?
  • Could blood loss, low oxygen levels or red cells breaking down explain this?
  • Should we check my hemoglobin, reticulocyte count and a blood smear?
  • Should we repeat this test, and when?

Questions people ask

Why does my report show nRBC as a % if it is per 100 white cells?

Labs print a % sign, but the count is per 100 white blood cells counted, not a share of red cells. So 'NRBC 1 %' means 1 nRBC for every 100 white cells.

Why did my white blood cell count change after nRBCs were found?

Many analyzers count nRBCs as white cells, so the first white count can read too high. When nRBCs are present, the lab subtracts them to give a corrected white count.

Are nRBCs normal in babies?

Yes. nRBCs are normal in a fetus and newborn, and in healthy babies they usually disappear within the first month. ARUP's interval for the first 3 days of life is 0.1 to 8.3 per 100 white cells. A newborn's care team interprets the result.

Show the science and sources

Units

  • 1 % (per 100 WBC) = 1 % (per 100 WBC)
  • 1 % (per 100 WBC) = 1 /100 WBC

For clinicians and researchers

Percent nRBC is the number of nucleated erythroid cells per 100 leukocytes counted (LOINC classes it as a ratio to leukocytes), not a share of red cells. Many analyzers count nRBCs as leukocytes, which falsely raises the WBC, so the WBC is corrected: corrected WBC = WBC x 100 / (100 + nRBC per 100 WBC). The level at which labs apply the correction varies (1, 5, 10, 20 or 50 per 100 WBC are all used, and 5 and 10 are the most common). Automated counting on the Sysmex XE-2100 and Cell-Dyn 4000 matched microscopic counts in newborn blood. At the extreme, one neonatal hemolytic disease case had more than 2,000 nRBCs per 100 WBC, with an analyzer WBC of 163 x10^9/L that fell to 28 after manual correction. Reference intervals: ARUP lists 0% from age 4 days (0.1 to 8.3% for ages 0 to 3 days, shown here with a lower limit of 0), Labcorp lists 0 to 0 above 30 days, and OHSU lists 0 to 0.3 at all ages. One health-system lab (MHCC) sends the slide to a pathologist when nRBCs exceed 3 per 100 WBC, or exceed 50 in babies under 7 days old. A 2026 meta-analysis of 20 cohorts (17,691 critically ill adults) linked nRBC positivity to higher 30-day mortality (OR 3.14), with very low certainty for several outcomes. This describes hospital patients, not outpatients.

LOINC 58413-6 (primary), 19048-8, 18309-5. Specimen: whole-blood.

Sources

  1. CBC with Platelet Count and Automated Differential (test 0040003), hotline effective March 1, 2021, ARUP Laboratories (2021)
  2. Pediatric Testing Reference Ranges, Labcorp
  3. CBC with Differential, Oregon Health & Science University (OHSU Lab Services)
  4. Complete Blood Count (CBC) With Differential, Reflex to Peripheral Smear Review (test 005009), Labcorp
  5. Complete Blood Count (CBC) with Automated Differential (test code CBCD), MHCC Laboratory (test catalog powered by Mayo Clinic Laboratories)
  6. Diagnostic Value and Prognostic Significance of Nucleated Red Blood Cells (NRBCs) in Selected Medical Conditions, Cells (2023)
  7. Cutoff Value for Correcting White Blood Cell Count for Nucleated Red Blood Cells: What is it? Why is it Important?, Laboratory Medicine (2019)
  8. Automated counting of nucleated red blood cells in blood samples of newborns, Clinical and Laboratory Haematology (2002)
  9. Peripheral blood nucleated red blood cells predict short-term mortality and clinical outcomes in critically ill adults: A systematic review and meta-analysis, Biomolecules & Biomedicine (2026)
  10. Challenges in interpreting leukocyte and nucleated red blood cell counts in neonatal hemolytic disease: A case report on hematology analyser performance, Journal of Medical Biochemistry (2026)

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

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