Nucleated Red Blood Cells: What They Mean in Adults
Medically reviewed by Dr. Michael Teplitsky, MD Last reviewed 2026-10-12
What finding immature red blood cells on a complete blood count can mean for adults
Nucleated red blood cells are immature erythroblasts that normally remain inside the bone marrow of healthy adults. When an automated analyzer or blood smear detects them in peripheral circulation, it can signal high demand for red cell production. Possible causes range from anemia and prolonged hypoxemia to bone marrow disorders that require medical follow-up.
Nucleated red blood cells (NRBCs) are immature red blood cells that normally stay in the bone marrow, so they are not expected in the blood of a healthy adult. Finding these cells in peripheral blood can mean the bone marrow is under high demand to make red cells, so that immature cells are released into circulation.
Because their appearance can stem from causes ranging from anemia to bone marrow disorders, finding them requires clinical follow-up rather than a conclusion from the number alone.
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See what Opt Health tests →What Nucleated Red Blood Cells Are
Nucleated red blood cells are progenitor cells of the red-cell lineage. They are also called erythroblasts or immature red cells. According to research in Frequency of nucleated red blood cells in ICU-admitted patients (PMC), nucleated red blood cells are normally absent from the peripheral blood of healthy people. Only newborns and premature infants have small amounts physiologically.
Possible Causes of Nucleated Red Blood Cells
- acute and chronic anemia
- prolonged hypoxemia (low blood oxygen)
- congestive cardiac failure
- miliary tuberculosis
- myelofibrosis
- thalassemia
- bone marrow malignancies (myeloma, leukemia, lymphoma)
- hypoxemia or infection in critically ill patients
Many conditions produce this finding, so the result needs a clinician's follow-up rather than a conclusion from the number alone.
How Nucleated Red Blood Cells Are Counted
Laboratories quantify nucleated red blood cells using automated hematology analyzers or manual microscopic reviews of stained blood smears. Automated analyzers are more practical for clinical laboratories and can often measure NRBC concentrations below 100 per microlitre. On a stained blood smear, concentrations below 200 per microlitre are challenging to find and may go undetected (false negatives).
What Research in Intensive Care Patients Shows
NRBCs may be a marker of severity in intensive care patients. A study published in Frequency of nucleated red blood cells in ICU-admitted patients (PMC) evaluated 800 critically ill intensive care unit (ICU) patients aged 18 to 70 in Lahore, Pakistan. Among these patients, 62.5 percent (500 of 800) tested positive for circulating nucleated red blood cells. This is an intensive-care population and does not describe outpatients with an incidental finding. Mortality was 30 percent (150 of 500) in NRBC-positive patients compared with 14 percent (44 of 300) in NRBC-negative patients. NRBCs may be a marker of severity, suggesting a high risk of death in intensive care patients, and are linked to possible bone marrow dysfunction or impaired red-cell production.
Getting the Blood Drawn
NRBCs are looked for in a blood sample, as with a blood differential or CBC. According to MedlinePlus, the sample is drawn from a vein in the arm with a small needle, usually in under five minutes. No special preparation is necessary and the risk is very low.
What to Do With Your Result
An abnormal test result does not always indicate a condition that requires medical treatment. As MedlinePlus explains, a healthcare provider considers your symptoms, medical history, and other diagnostic tests before determining a diagnosis. The reference range printed on your own report applies.
Review our blood test results guide and consult your physician to interpret the presence of nucleated red blood cells in your blood.
Where to Find CBC Test Kits
Many labs and direct-to-consumer services let you order a CBC (complete blood count) test without a doctor's visit. If you'd rather compare kits yourself, here's where to start looking:
- At-home CBC (complete blood count) test kits on Amazon — compare brands, prices, and Prime shipping.
Frequently Asked Questions
What are nucleated red blood cells?
Nucleated red blood cells (NRBCs), also called erythroblasts, are immature progenitor cells of the red-cell lineage. They are normally absent from adult circulation, appearing physiologically only in newborn and premature infants.
Are nucleated red blood cells normal in adults?
No, nucleated red blood cells are not normal in the blood of healthy adults. Finding them can mean the bone marrow is under very high demand to make red cells, so that immature cells are released into circulation.
What causes high NRBCs?
High NRBCs in adults can stem from acute or chronic anemia, prolonged hypoxemia (low blood oxygen), congestive cardiac failure, or miliary tuberculosis. Other listed causes are myelofibrosis, thalassemia, and bone marrow malignancies (myeloma, leukemia, lymphoma), and infection in critically ill patients.
Does NRBC mean leukemia?
A finding of nucleated red blood cells is not a diagnosis of leukemia. Bone marrow malignancies such as leukemia, lymphoma, and myeloma are among many listed causes, which also include acute and chronic anemia, low blood oxygen, and congestive cardiac failure. A provider must evaluate your full clinical history and additional tests before establishing a diagnosis.
Should nucleated red blood cells be zero on a CBC?
Nucleated red blood cells are normally absent from the blood of healthy people. However, the specific reference range on your laboratory report governs your results, and any abnormal finding should be evaluated by a healthcare provider alongside your symptoms and history.
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