University of Virginia Health System

Pronormoblast
(Proerythroblast, Rubrioblast)

Bone marrow aspirate smear, Wright-Giemsa stain, 1000x

Description:

The pronormoblast is the earliest red cell (erythroid) precursor identifiable by light microscopy on a Wright-Giemsa stain of a bone marrow aspirate. The pronormoblast is easily distinguished from other "blasts". It is larger "diameter", 12-20 μm, the nucleus is centrally located, usually round, and surrounded by dark blue (basophilic) cytoplasm. At this and the basophilic normoblast stage, cytoplasmic blebs resembling "Mickey Mouse ears" are not infrequently noted. The nuclear chromatin has a fine to slightly coarse granular appearance, is evenly dispersed, and minimal parachromatin is seen. Two or more nucleoli surrounded by condensed chromatin are usually visible. From this stage on in the maturation process, the overall size of the cell decreases as does the nuclear:cytoplasm ratio. The intensity of the basophilic cytoplasm decreases as more and more hemoglobin is synthesized until the orthochromatic stage where the cytoplasm has a light grey-pink color, similar to that of a reticulocyte.

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