Nucleated red blood cells (NRBCs) are immature forms of red blood cells that typically remain within the bone marrow during their development. These cells are not usually detected in the bloodstream of healthy adults. Their presence in circulation generally signifies an underlying health condition that requires medical attention.
What Are Nucleated Red Blood Cells?
Nucleated red blood cells (NRBCs), also known as erythroblasts, are precursors to mature red blood cells. They contain a nucleus, unlike the biconcave, anucleated mature red blood cells that circulate throughout the body.
During their normal maturation, NRBCs lose their nucleus before being released into the peripheral bloodstream. This enucleation allows mature red blood cells to achieve their characteristic shape and flexibility, optimizing oxygen transport. The spleen removes any remaining NRBCs that might inadvertently enter circulation, preventing their persistence in the bloodstream.
Understanding the Normal Range
The normal range for nucleated red blood cells in adults is zero. Most laboratories report the absence of NRBCs per 100 white blood cells (WBCs) as the standard healthy finding. While some clinical settings may define an extremely low level as normal, such as 0% to 0.5% of total WBCs, even a small number of NRBCs, when detected, holds clinical significance, prompting further investigation into a person’s health status.
Why Nucleated Red Blood Cells Appear in Adults
The appearance of nucleated red blood cells in the bloodstream of adults indicates that the bone marrow is under significant stress or is compromised, releasing these immature cells prematurely.
Severe Anemia
One common cause is severe anemia, particularly conditions like hemolytic anemia, where red blood cells are destroyed at an accelerated rate. The bone marrow responds by rapidly producing and releasing new red blood cells, including immature forms, to compensate for the loss.
Hypoxia
Conditions that cause low oxygen levels in the body, known as hypoxia, also stimulate the release of NRBCs. When tissues are deprived of adequate oxygen, the kidneys produce erythropoietin, a hormone that signals the bone marrow to increase red blood cell production. This heightened demand can lead to the premature release of nucleated forms. Chronic respiratory diseases or severe heart conditions can lead to such hypoxic states.
Spleen Dysfunction or Removal
Dysfunction or removal of the spleen can contribute to NRBC presence, as the spleen normally filters out and removes these immature cells from circulation. If the spleen is not functioning properly or has been surgically removed, NRBCs may persist in the bloodstream.
Bone Marrow Damage or Infiltration
Damage or infiltration of the bone marrow itself can also result in NRBCs entering circulation. Conditions such as myelofibrosis, where fibrous tissue replaces normal bone marrow, or the presence of metastatic cancer cells within the bone marrow, can disrupt normal red blood cell maturation and release. Blood cancers like leukemia, which involve uncontrolled proliferation of abnormal white blood cells, can also crowd out normal blood cell production and lead to the release of immature red blood cell forms. Severe infections or widespread inflammation place immense stress on the bone marrow, sometimes triggering an accelerated release of all blood cell types, including NRBCs, as part of the body’s generalized response.
Nucleated Red Blood Cells in Newborns and Children
The presence of nucleated red blood cells in newborns is a normal physiological finding, especially immediately after birth. This is because the fetal and neonatal bone marrow is highly active in producing red blood cells, and the transition to mature red blood cell production is still underway. The frequency of circulating NRBCs in infants gradually declines over the first few weeks of life, reaching near zero around one month of age.
Elevated NRBC counts in newborns, beyond expected physiological levels, signal health concerns. High levels indicate neonatal hypoxia, a state of insufficient oxygen at birth, or other adverse perinatal events. Monitoring NRBC counts in neonates serves as a marker for the severity of perinatal distress and correlates with increased risks of infant mortality or long-term neurological complications.
Interpreting Nucleated Red Blood Cell Results
Interpreting nucleated red blood cell results requires a comprehensive approach, integrating the findings with other components of a complete blood count (CBC). This includes evaluating red blood cell count, white blood cell count, hemoglobin levels, and a differential count of white blood cells. The overall clinical picture of the patient, including their symptoms, medical history, and any other diagnostic test results, provides further context.
A healthcare professional considers the absolute number of NRBCs and their proportion relative to other blood cells when making a diagnosis. The presence of these immature cells is rarely interpreted in isolation; instead, it serves as one piece of information that contributes to a broader understanding of a person’s hematological status. Consulting a physician or hematologist is for accurate diagnosis and appropriate treatment planning based on all available data.