Red blood cells are microscopic, disc-shaped cells responsible for transporting oxygen throughout the body. They typically lack a nucleus in their mature form, allowing them to carry more hemoglobin, the protein that binds oxygen. Nucleated red blood cells (NRBCs) are immature forms of these cells that still retain their nucleus. Their presence in the bloodstream can signal underlying health conditions.
What Are Nucleated Red Blood Cells?
Nucleated red blood cells (NRBCs), also known as erythroblasts or normoblasts, are immature red blood cells that still possess a nucleus. Unlike mature red blood cells, which lose their nucleus before entering circulation, NRBCs are a normal part of red blood cell development within the bone marrow. This maturation process involves the gradual expulsion of the nucleus, allowing the cell to become more flexible and efficient at carrying oxygen.
In healthy adults and children beyond infancy, NRBCs are confined to the bone marrow. Their presence in the peripheral blood is considered an abnormal finding, indicating a disruption in the normal maturation and release process. However, NRBCs are a normal finding in the blood of fetuses and newborn infants, usually disappearing within the first few weeks of life as their blood production system matures.
Why Do Nucleated RBCs Appear in the Blood?
The appearance of nucleated red blood cells in the bloodstream of adults indicates that the bone marrow is under stress or functioning abnormally. One reason is an increased demand for red blood cell production, such as in cases of severe anemia or acute blood loss. When the body needs to replace red blood cells rapidly, the bone marrow may release these immature forms into circulation prematurely.
Conditions like hemolytic anemia, where red blood cells are destroyed faster than they can be produced, can lead to this accelerated release. Bone marrow stress can also result from chronic low oxygen levels, known as hypoxemia, which stimulates the bone marrow to work overtime. Damage to the bone marrow, or its infiltration by diseases like myelofibrosis or some cancers, can also impair its ability to properly mature red blood cells before releasing them.
What Their Presence Signifies
The presence of nucleated red blood cells in an adult’s blood indicates an underlying medical issue. While not a diagnosis itself, it serves as a marker that something is affecting red blood cell production or survival. One common condition it can signify is severe anemia, including types like sickle cell crisis or thalassemia, where the body struggles to maintain adequate red blood cell levels.
NRBCs can also point to bone marrow disorders such as myelodysplastic syndromes or leukemias, which directly impact the bone marrow’s ability to produce healthy blood cells. Their appearance can also be linked to conditions causing systemic stress, such as major infections, organ failure, or trauma. In intensive care unit (ICU) patients, the presence of NRBCs has been associated with longer hospital stays and increased mortality rates, highlighting their prognostic value.
Detection and Clinical Evaluation
Nucleated red blood cells are detected during a routine complete blood count (CBC) with a manual differential, which involves examining a peripheral blood smear under a microscope. Automated blood analyzers can also flag the presence of NRBCs, though they may sometimes be misidentified as white blood cells, necessitating manual confirmation. The count is reported as a percentage of white blood cells or as an absolute number.
If NRBCs are identified in an adult’s blood, further diagnostic steps are initiated to pinpoint the underlying cause. These follow-up tests vary depending on the suspected condition but may include specialized blood tests to determine the type of anemia, or a bone marrow biopsy to examine the bone marrow’s health and cellular composition. Imaging studies or other diagnostic procedures may also be performed as part of a comprehensive evaluation.