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

Monocyte*


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› Microscopic Features:

• 3-4x larger than a mature RBC
• Lower nuclear to cytoplasmic ratio because of increased cytoplasm
• Kidney shaped Indented Nucleus with mature chromatin (clumped)
• Nucleoli are absent
• Cytoplasm is abundant, gray to pale blue and with rare to no granules
• vacuoles are commonly noted in cytoplasm

› Normal % blood-PB, marrow-BM, lymphoid tissue-LN:

• PB: Monocytes are the 3rd most common WBC in the blood (after neutrophils and lymphocytes)
• BM: Scattered monocytes can be seen in the bone marrow (some in the form of histiocytes/macrophages)
• LN: Scattered monocytes can be seen in the bone marrow (some in the form of histiocytes/macrophages)

› May Resemble:

• Reactive lymphocyte [Compare]
• Myelocyte [Compare]
• Metamyelocyte [Compare]
• Band Neutrophil [Compare]
• Promonocyte [Compare]
• Monoblast [Compare]

› Differential Diagnoses:

If increased in blood or increased numbers in bone marrow: Chronic Myelomonocytic Leukemia Autoimmune disorders (sometimes) Chronic infections (e.g. CMV, tuberculosis, etc.)

› Classic Immunophenotype:

• CD45+
• Intermediate SSC (Side light scatter)
• CD14+
• CD4dim+
• CD64+

› Cartoon Image:


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› Misc:

• Monocytes leave the blood and enter tissue to become macrophages/histiocytes