Myelocyte

A myelocyte is a young cell of the granulocytic series, occurring normally in bone marrow, but not in circulating blood (except when caused by certain diseases).

Histology
When stained with the usual dyes, the cytoplasm is distinctly basophilic and relatively more abundant than in myeloblasts or promyelocytes, even though myelocytes are smaller cells.

Numerous cytoplasmic granules are present in the more mature forms of myelocytes. Neutrophilic and eosinophilic granules are peroxidase-positive, while basophilic granules are not.

The nuclear chromatin is coarser than that observed in myelocyte, but it is relatively faintly stained and lacks a well defined membrane.

The nucleus is fairly regular in contour (not indented), and seems to be 'buried' beneath the numerous cytoplasmic granules. (If the nucleus were indented, it would likely be a metamyelocyte.)

Maturation
Myelocytes are derived from promyelocytes and give rise to metamyelocytes.

Measurement
There is an internationally agreed method of counting blasts, with results from M1 upwards.