Nucleated Red blood cells (NRBCs) are not normally found in healthy adults because mature RBCs do not have a nucleus. However, they may be present with a hematological disease, significant blood loss, or hemolysis.
Nucleated RBCs are precursors to reticulocytes which then mature into erythrocytes (RBCs). Mature RBCs do not have a nucleus. Therefore, NRBCs in circulation indicate early release from the bone marrow. This can occur with the rapid replacement of RBCs (hemolysis or blood loss) or hematological diseases such as chronic myeloid leukemia, acute leukemia, and myelodysplastic syndromes. NRBCs are a type of erythroblast.
An increase in NRBCs may also occur during chemotherapy, inflammation, hypoxia, and other causes of hematopoietic stress. They can also be present in newborns for the first few months of life. However, sustained levels in adults may indicate an increased risk of mortality. The finding of NRBCs above 220 cells/uL was associated with a 3-times greater risk of death in intensive care patients.
NRBCs should be “zero” or zero percent, and their presence should be investigated further.
Reference
May, Jori E et al. “Three neglected numbers in the CBC: The RDW, MPV, and NRBC count.” Cleveland Clinic journal of medicine vol. 86,3 (2019): 167-172. doi:10.3949/ccjm.86a.18072