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Hematology: nucleated red blood cells

ISSN 2398-2985

Synonym(s): Rubricytes, Normoblasts, Erythroblasts, Metarubricytes


  • Red cells are produced in the bone marrow.
  • Total maturation time in erythrocytes is 5-10 days in most species.
  • When there is an increased demand for red cells (hemorrhage, hypoxia) the production is increased firstly by allowing younger forms to enter the circulation, and secondly by allowing the maturation stages to merge and skip so that erythropoiesis speeds up.
  • Normoblasts and different stages of erythroblasts possess nucleus. Reticulocytes (polychromatophilic macrocytes) and normocytes (erythrocytes) do not possess nucleus.
  • Forms that precede reticulocytes are nucleated red blood cells (nucleated RBCs).
  • Nucleataed RBCs are larger than normal red blood cells, and often polychromatic. They resemble lymphocytes, but nucleus smaller and denser and cytoplasm abundant and pink-tinged. However, morphology and staining characteristics may be variable.
  • Elevation in the numbers of nucleated RBCs is always significant and may increase MCV (Mean Corpuescular Volume) and RDW (Red blood cell Distribution Width).
  • Usually seen as part of a regenerative response to anemia or hypoxemia.



  • Indicative of increased demand for RBCs.

In combination

  • With other RBC indices and parameters for investigation of anemia Anemia overview.
  • May be associated with imperfect erythrocytes in circulation, such as Howell-Jolly bodies, poikilocytes and leptocytes.


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  • See Hematology: leukocyte (WBC) Hematology: leukocyte (WBC).
  • Romanowsky stain.
  • New Methylene Blue stain.
  • Electronic cell counters are not reliable identifying nucleated RBCs. High number of nucleated RBCs may not be differenciated from lymphocytosis/monocytosis using electronic cell counters.


  • Hematologic stains are widely available at commercial laboratories.
  • Blood smear examination can be performed in practice.



  • Depends on experience of cytologist in recognizing cells.


  • Good.

Predictive value

  • High - always significant finding if in large numbers.

Technician extrinsic limitations

  • Require some cytological experience to identify cells accurately.

Result Data

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Further Reading


Refereed Papers

Other sources of information

  • Campbell T W & Ellis C K (2007) Avian and Exotic Hematology and Cytology. 3rd edn. Wiley-Blackwell. ISBN: 978-0813818115.