Note that the mature forms of the myeloid series
(neutrophils, eosinophils, basophils), all have lobed
(segmented) nuclei. The degree of lobation increases as the
Starting with the cell at the LEFT, CLICK on the above
images to review WBC maturational morphology.
The earliest recognizable myeloid cell is the myeloblast
(10-20m dia) with a large round to oval nucleus. There is
fine diffuse immature chromatin (without clumping) and a
The cytoplasm is basophilic without granules. Although
one may see a small golgi area adjacent to the nucleus,
granules are not usually visible by light microscopy. One
should not see blast cells in the peripheral blood.
The promyelocyte (10-20m) is slightly larger than a
blast. Its nucleus, although similar to a myeloblast shows
slight chromatin condensation and less prominent nucleoli.
The cytoplasm contains striking azurophilic granules or
primary granules. These granules contain myeloperoxidase,
acid phosphatase, and esterase enzymes. Normally no
promyelocytes are seen in the peripheral blood.
At the point in development when secondary granules can
be recognized, the cell becomes a myelocyte.
Myelocytes (10-18m) are slightly smaller than
promyelocytes and have eccentric round-oval nuclei, often
flattened along one side. The chromatin is fine, but shows
evidence of condensation. Nucleoli may be seen in early
stages but not in the late myelocyte. Primary azurophilic
granules are still present, but secondary granules
predominate. Secondary granules (neut, eos, or baso) first
appear adjacent to the nucleus. In neutrophils this is the
"dawn" of neutrophilia.
Myelocytes are not normally found in the peripheral
Metamyelocytes (10-18m) are slightly smaller than
myelocytes. They have kidney shaped indented nuclei and
relatively dense chromatin, especially along the nuclear
membrane. The cytoplasm is faintly pink with almost no blue
background. Numerous secondary granules (neutro, eos, or
baso) clearly outnumber primary granules. Zero to one
percent of the peripheral blood white cells may be
Bands, slightly smaller than juveniles, are marked by a
U-shaped or deeply indented nucleus. Opposite sides or lobes
are of roughly equal size or diameter. There is no nuclear
constriction > than 1/2 the lobe diameter. The chromatin
is heavily clumped and secondary or specific granules either
neutrophilic or basophilic predominate.
Normal band counts vary but are usually in the range of
Segmented (segs) or polymorphonuclear (PMN) leukocytes
(average 14 m dia) are distinguished by definite lobation
with thin thread-like filaments of chromatin joining the 2-5
lobes. The chromatin of the segmented neutrophil is coarsely
clumped and the cytoplasm is pink due to large numbers of
In practice when examining peripheral blood, neutrophils
are the only leukocytes to be divided into myelocyte,
juvenile, band, and PMN stages. Eosinophils and basophils of
all stages are lumped together in most instances.
Normally approximately 45-75% of the peripheral blood
white cells are segmented neutrophils.
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