Normal Erythrocyte Morphology

The maturation process of red blood cells begins in the bone marrow where the first four identifiable stages of maturation: pronormoblast, basophilic normoblast, polychromatophilic normoblast, and orthochromatic normoblast are normally found. The presence of any of these stages in the peripheral blood should be considered for further evaluation. Table 2 provides brief descriptions of the expected morphology for all stages of red blood cell maturation.⁴

Table 2. Normal Morphology of Erythrocyte Stages.*

Stage	Found In BM/PB	Size and N:C Ratio	Nucleus	Cytoplasm
Pronormoblast	BM	14-24 µm 8:1-6:1	Round, central Dark blue/purple, stippled chromatin pattern 0-2 Nucleoli	Scant Deeply blue or royal blue No granules
Basophilic Normoblast	BM	12-27 µm 6:1-4:1	Round, central Chromatin pattern is more condensed Occasional indistinct or no nucleoli	Slightly basophilic cytoplasm No granules
Polychromatophilic Normoblast	BM	10-15 µm 4:1-2:1	Round, central Dark blue, smaller with increased clumped chromatin and more parachromatin visible No nucleoli	Moderate amount of bluish-pink cytoplasm No granules
Orthochromatic Normoblast	BM	8-12 µm 1:1-1:2	Round, central Dark blue/purple with condensed chromatin and pyknotic degeneration No nucleoli	Moderate amount of pink cytoplasm with slight blue tint No granules
Reticulocyte	BM/PB	7-10 µm N/A	N/A	Pink-orange with slight blue tint/ polychromatophilic No granules
Erythrocyte	BM/PB	7-8 µm N/A	N/A	Pink-orange biconcave disk with central pallor

*Modified from Harmening, Table 1-6, page 15