What are metamyelocytes?

Medical Advisory BoardAll articles are reviewed for accuracy by our Medical Advisory Board
Educational purpose only • Exercise caution as content is pending human review
Article Review Status
Submitted
Under Review
Approved

Last updated: February 18, 2026 • View editorial policy

Personalize

Help us tailor your experience

Which best describes you? Your choice helps us use language that's most understandable for you.

What Are Metamyelocytes

Metamyelocytes are immature granulocytes (neutrophil precursors) that represent an intermediate stage of myeloid maturation between myelocytes and band cells in the bone marrow, characterized by an indented or kidney-shaped nucleus and the presence of specific (secondary) granules. 1, 2

Position in Granulocyte Maturation Sequence

Metamyelocytes occupy a specific developmental stage in the neutrophil lineage:

  • They follow myelocytes and precede band cells in the normal maturation sequence from myeloblast → promyelocyte → myelocyte → metamyelocyte → band cell → segmented neutrophil. 2, 3

  • Metamyelocytes are classified within the "intermediate mature" population along with myelocytes when bone marrow cells are categorized by maturation stage. 3

  • This stage marks the point where cell division ceases in normal granulopoiesis, as metamyelocytes no longer undergo mitosis and continue maturation without further proliferation. 3

Morphologic and Phenotypic Characteristics

Nuclear Features

  • The nucleus becomes indented or kidney-shaped, distinguishing metamyelocytes from the round nucleus of myelocytes and the horseshoe-shaped nucleus of band cells. 2, 4

Cytoplasmic Granules

  • Metamyelocytes contain predominantly specific (secondary) granules with less electron-dense matrix, which were formed during the myelocyte stage. 4

  • They retain some azurophil (primary) granules formed earlier during the promyelocyte stage, creating a mixed granule population. 4

Surface Markers

  • Metamyelocytes express intermediate levels of CD16, which helps distinguish them from earlier stages (CD16-negative) and mature neutrophils (CD16-strongly positive). 2

  • They are part of the CD11b-positive myeloid population but lack the full complement of mature neutrophil surface markers. 2

Clinical Significance

Normal Bone Marrow

  • Metamyelocytes are normally confined to the bone marrow and should not appear in significant numbers in peripheral blood under physiologic conditions. 1

Pathologic Conditions

When metamyelocytes appear in peripheral blood (as part of immature granulocytes), this indicates:

  • Enhanced bone marrow activity with "left shift" in response to severe infection, inflammation, or stress. 1

  • Chronic myeloid leukemia (CML), where the hallmark finding is leukocytosis with immature granulocytes including metamyelocytes, myelocytes, and promyelocytes, along with basophilia. 5, 6

  • Severe systemic conditions such as sepsis, severe acute pancreatitis, or systemic inflammatory response syndrome where increased immature granulocyte counts correlate with disease severity. 1

Diagnostic Utility

  • In CML specifically, the presence of metamyelocytes along with the full spectrum of myeloid maturation (from blasts to mature neutrophils) is characteristic, distinguishing it from acute myeloid leukemia which lacks orderly maturation. 5, 6

  • Immature granulocyte counts (including metamyelocytes) serve as biomarkers of disease severity in conditions like COVID-19 infection, where higher counts correlate with worse outcomes, longer hospitalization, and increased mortality risk. 1

Transcriptional Profile

  • Metamyelocytes show peak expression of C/EBP-epsilon, which is almost absent in more mature cells, making this transcription factor a molecular marker of this specific maturation stage. 3

  • Expression of C/EBP-beta, C/EBP-delta, and C/EBP-zeta begins at the metamyelocyte stage and increases with further maturation. 3

References

5
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

6
Guideline

Differentiating AML from CML on CBC

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

Related Questions

What is the significance of metamyelocytes on a peripheral blood smear and how should they be evaluated and managed?
What are metamyelocytes?
What is the clinical approach to a patient with metamyelocytes in the peripheral blood?
What are the next steps for a patient with thrombocytopenia, elevated immature granulocytes, and macrocytosis?
What causes high granulocytes?
Which fast‑acting medication is appropriate for acute anxiety in an adult without contraindications such as severe respiratory disease, uncontrolled glaucoma, pregnancy, substance‑use disorder, or severe hepatic impairment for short‑term use?
Can metoprolol be prescribed to a breastfeeding mother?
Can any steroid other than methylprednisolone be used in acute demyelinating encephalitis?
Can an adult with osteoporosis undergo palatal expansion?
What is the appropriate management for a woman in her late 80s with anemia (hemoglobin 8.4 g/dL) and a left ventricular ejection fraction of about 30%?
For an adult stable patient without severe renal or hepatic impairment receiving 20 units regular insulin with 215 g dextrose in a total parenteral nutrition (TPN) bag over a 24‑hour cycle, how many insulin units should be added when the TPN cycle is shortened to 18 hours while keeping the total dextrose unchanged?

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

Have a follow-up question?

Our Medical A.I. is used by practicing medical doctors at top research institutions around the world. Ask any follow up question and get world-class guideline-backed answers instantly.

Ask Question