1 Red Blood Cell Maturation

Michelle To and Valentin Villatoro

Pronormoblast (Rubriblast, Proerythroblast)

Notes: Largest of the RBC maturation series 1


Nucleus-to-Cytoplasm Ratio: 8:1 (High) 1,2


Nucleoli: 0-2 2,3 



Round to oval, central

Fine, homogeneous chromatin

Reddish-blue colour under Wright stain



Small to moderate amount of cytoplasm

Dark blue cytoplasm (due to large RNA content)

Golgi may be seen (pale area next to the nucleus)


% in Bone Marrow: 1%  1-3

Basophilic Normoblast (Prorubricyte, Basophilic Erythroblast)

Notes: Smaller than Pronormoblasts 3


Nucleus-to-Cytoplasm Ratio: 6:1 1


Nucleoli: 0-1 2


Nucleus:  1-3 

Round to slightly oval, central

Chromatin is coarser and slightly clumped

Dark violet in colour

Indistinct nuclei or not visible


Cytoplasm: 1,2

Dark blue (due to large RNA content)

May see a perinuclear halo (unstained mitocondria)

May have a slight pink tinge due to the production of hemoglobin


% in Bone Marrow: 1-5% 

Polychromatic Normoblast (Rubricyte, Polychromatic Erythroblast)

Notes: Last RBC maturation stage capable of mitosis 1


Nucleus-to-Cytoplasm Ratio: 4:1 1-3 


Nucleoli: None 2


Nucleus: 1-3

Round, eccentric

Chromatin is coarse, irregularly clumped


Cytoplasm: 1,2


Gray-blue to pink (due to hemoglobin production and RNA content)


% in Bone Marrow: 5-30% 3


% in Peripheral Blood: Normally NOT present in the peripheral blood but some may be seen in the peripheral blood smears of newborns.3

Orthochromic Normoblast (Metarubricyte, Orthochromatic Erythroblast)

Notes: The smallest RBC precursor and incapable of further DNA synthesis at this stage.3


Nucleus-to-Cytoplasm Ratio: 1:1 (Low) 3


Nucleoli: None 2-3


Nucleus: 1,2

Round, eccentric

Fully condensed chromatin with pyknotic features


Cytoplasm: 1,2

Pink or salmon; May appear slightly blue due to residual RNA


% in Bone Marrow: 5-10% 2


% in Peripheral Blood: Normally NOT present in the peripheral blood but some may be seen in the peripheral blood smears of newborns. 3

Reticulocyte (Polychromatic Erythrocyte, Diffusely Basophilic Erythrocyte)

Notes: the nucleus has now been expelled from the cell, residual RNA gives the cell a polychromatic appearance. The use of supravital stains can help to identify and enumerate Reticulocytes by visualizing reticular inclusions (linear granulation, with a “beads on a string” appearance, see figure below). (Har ch 1 pg 13)


Nucleus-to-Cytoplasm Ratio: N/A 2


Nucleoli: N/A 2


Nucleus: N/A  2


Cytoplasm:  2,3 

Light blue-purple to pink (due to residual RNA content and high hemoglobin content)


% in Bone Marrow: 1%  2


% in Peripheral Blood: 0.5-2%  2

Erythrocyte (Discocyte)

Notes: The mature red blood cell is biconcave in shape and lacks ribosomes and mitochondria; therefore, it lacks the ability to synthesize proteins such as hemoglobin and enzymes such as G6PD.1


Nucleus-to-Cytoplasm Ratio: N/A 2


Nucleoli: N/A  2


Nucleus: N/A  2


Cytoplasm:  2-3

Pink-salmon colour with an area of central spanning one-third of the diameter. Cell should contain no inclusions.


% in Bone Marrow: N/A  2


% in Peripheral Blood: Predominant 2


1. Robinson S, Hubbard J. The erythrocyte. In: Clinical laboratory hematology. 3rd ed.  New Jersey: Pearson; 2015. p. 59-76.

2. Rodak BF, Carr JH. Erythrocyte maturation. In: Clinical hematology atlas. 5th ed. St. Louis, Missouri: Elsevier Inc.; 2017. p. 17-30

3. Bell A, Harmening DM, Hughes VC. Morphology of human blood and marrow cells. In: Clinical hematology and fundamentals of hemostasis. 5th ed. Philadelphia: F.A. Davis Company; 2009. p. 1-41.


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Red Blood Cell Maturation Copyright © 2019 by Michelle To and Valentin Villatoro is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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