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Although nucleated red blood cells (nRBCs) are rarely found circulating in older children,1 they are commonly seen in the blood of newborns. They are primarily produced in the fetal bone marrow in response to erythropoietin and are stored in the marrow as precursors to reticulocytes and mature erythrocytes. Many acute and chronic stimuli cause increases in the number of circulating nRBCs from either increased erythropoietic activity or a sudden release from the marrow storage pools. This paper reviews the various pathological processes associated with increased production and release of nRBCs. It emphasises the effects of acute, subacute, and chronic asphyxia on nRBC counts.
Key message
1
Common causes of increased nucleated red blood cells include prematurity, increased erythropoiesis from chronic hypoxia, anaemia, and maternal diabetes, from acute stress mediated release from the marrow stores, and from postnatal hypoxia. Extreme increases may occasionally be idiopathic.
Key message
2
When increased nRBC counts are seen with acute and subacute asphyxia, the magnitude of the increase is a function of the severity and duration of the asphyxia. However, there is a large overlap between the nRBC values found after acute, subacute, and chronic asphyxia; asphyxia of any duration does not always cause an increased nRBC count, and extreme increases may be found without asphyxia.
Nucleated red blood cells are sometimes called erythroblasts, normoblasts, or normocytes. For this review, the term “normoblasts” will be used to refer to the cells when they are in the bone marrow and “nRBCs” when they are in circulating blood.
Units of reporting
Clinically it is best to express nRBCs as an absolute number of cells per unit volume, either “nRBCs/mm3” or “nRBCs/l”. However, most clinical laboratories and many research publications report nRBCs relative to 100 white blood cells (WBCs). Unfortunately the extreme variability in the number of leucocytes …