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

Metamyelocyte*


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› 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 [Compare]
• Myelocyte [Compare]
• Band Neutrophil [Compare]
• Monocyte [Compare]
• Reactive lymphocyte [Compare]

› 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:


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for direct comparison
› Misc:

• Increased number of metamyelocytes are also typically noted in CML patients