Primary Hematopoietic and Lymphoid Tissue ›› Bone Marrow ›› Normal

Myelocyte*






Microscopic Features:
  • 2-3x larger than a mature RBC
  • Intermediate nuclear to cytoplasmic ratio (more cytoplasm than promyelocyte)
  • Eccentrically placed oval Nucleus (No nucleus indentation) with more mature chromatin (clumped)
  • Perinuclear clearing is common
  • Nucleoli are absent (Note: absent nucleoli from this stage onward)
  • More cytoplasm with only rare or absent primary (azurophilic) granules
  • Secondary (specific) granules of neutrophilic (lilac), eosinophilic (red-orange), or basophilic (blue) color are present based on precursor type
Normal % blood-PB, marrow-BM, lymphoid tissue-LN:
  • PB: None
  • BM: Scattered (~10%)
  • LN: None
May Resemble:
  • Promyelocyte
  • Metamyelocyte
  • Monocyte
  • Reactive lymphocyte
  • Plasma cell
Differential Diagnoses:

If in blood or increased numbers in bone marrow:
Chronic Myelogenous Leukemia (CML)
Leukemoid reaction
Post-GCSF therapy
Chronic Neutrophilic Leukemia

Classic Immunophenotype:
  • CD34-
  • CD117-
  • HLA-DR-
  • CD13+
  • CD33+
  • CD15+
  • CD11b+/-
  • CD16-
Cartoon Image:



Misc:
  • Myelocyte bulge (increased myelocytes) is commonly noted in CML patients