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

Metamyelocyte*






Microscopic Features:
  • 2-3x larger than a mature RBC
  • Intermediate nuclear to cytoplasmic ratio (more cytoplasm than promyelocyte)
  • Kidney bean-shaped Nucleus with nucleus indentation (indentation is less than 1/2 the diameter) and mature chromatin (clumped)
  • Perinuclear clearing is common
  • Nucleoli are absent
  • More cytoplasm with only secondary 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 (~10-15%)
  • LN: None
May Resemble:
  • Promyelocyte
  • Myelocyte
  • Band Neutrophil
  • Monocyte
  • Reactive lymphocyte
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:
  • Increased number of metamyelocytes are also typically noted in CML patients