myelocyte

Myelocyte is an intermediate cell in granulopoiesis, the process by which granulocytes (neutrophils, eosinophils, and basophils) are produced in the bone marrow. It follows the promyelocyte stage and precedes the metamyelocyte stage. During normal hematopoiesis, cell division largely ceases by the myelocyte stage, with maturation proceeding to metamyelocytes, band cells, and finally mature granulocytes.

Morphology and characteristics: Myelocytes are typically 12–18 micrometers in diameter, with a round to oval nucleus that is more condensed than in earlier precursors and often shows a slight indentation. The cytoplasm begins to contain specific (secondary) granules that are characteristic of the granulocyte lineage, while primary (azurophilic) granules are diminished compared with promyelocytes. The cytoplasm is generally less basophilic than in promyelocytes and may appear lighter as maturation progresses. The exact appearance can vary depending on whether the lineage is neutrophilic, eosinophilic, or basophilic.

Clinical and developmental significance: In normal marrow, myelocytes reside in the maturation compartment and are not typically seen in peripheral blood. Their presence in circulation can indicate a left shift or hematologic pathology, such as an infection, inflammatory condition, or myeloproliferative disorder. In bone marrow assessments, quantifying myelocytes helps evaluate granulopoiesis and marrow function, contributing to diagnoses of hematologic diseases.