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

Orthochromic Normoblast*


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› Microscopic Features:

• 1.5-2x larger than a mature RBC
• Low nuclear to cytoplasmic ratio
• Round Nucleus (sometimes eccentric) with pyknotic chromatin (dark & dense)
• Nucleoli are NOT seen
• Cytoplasm is grayish-orange in color

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

• PB: None
• BM: Many
• LN: None

› May Resemble:

• Lymphocyte (mature) [Compare]
• Polychromatophilic normoblasts [Compare]
• Plasma cell [Compare]

› Differential Diagnoses:

Increased in: Reactive Erythroid hyperplasia Post-erythropoietin therapy Polycythemia Vera

› Classic Immunophenotype:

• CD45-
• CD117-
• CD235a (Glycophorin A) +
• CD71+

› Cartoon Image:


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› Misc:

• Normally confined in bone marrow where they comprise many of the nucleated red blood cell precursors.Note: As Erythroid precursors mature, the color of their cytoplasm changes from blue to gray to red-orange (this is due to the increase in number of hemoglobin molecules within the red cells as they mature). Additionally, the nucleus of the red blood cell will become more dense as it matures, eventually excreting from the cell forming the mature RBC.