Medical Laboratory Scientist (MLS) ASCP Practice Exam

The correct answer is the promyelocyte, which is a stage in the maturation process of myeloid cells, specifically granulocytes. The myeloblast is the earliest identifiable precursor in the myeloid lineage, and it evolves through various stages, ultimately giving rise to the promyelocyte.

The promyelocyte itself is characterized by the formation of primary granules and an increase in cytoplasmic volume compared to the myeloblast. This stage is crucial because it marks the transition from an undifferentiated precursor to a more specialized cell type capable of further differentiation into neutrophils, eosinophils, or basophils. This differentiation is essential for the immune response, as granulocytes play critical roles in fighting infections and inflammation.

Monoblasts, erythrocytes, and megakaryocytes do not derive from myeloblasts. Instead, monoblasts are precursors to monocytes, erythrocytes are mature red blood cells derived from erythroblasts, and megakaryocytes are large cells responsible for the production of platelets, derived from the megakaryocyte lineage. Thus, understanding the lineage and differentiation pathways of these cell types is fundamental in hematopoiesis and the broader context