From the Research
The presence of metamyelocytes and myelocytes in the peripheral blood is a sign of left shift, indicating bone marrow stress or disease, and warrants further investigation, including complete blood count with differential and bone marrow examination if appropriate. This finding suggests that immature white blood cells are being released prematurely from the bone marrow into the bloodstream. The most common cause is acute infection or inflammation, where the body needs more white blood cells to fight pathogens, forcing the bone marrow to release immature forms. Other causes include leukemia, myeloproliferative disorders, myelodysplastic syndromes, or bone marrow infiltration by cancer, as seen in a case of hepatosplenic gamma delta T-cell leukemia/lymphoma 1.
The severity and clinical significance depend on the quantity of immature cells and the patient's overall clinical picture. For example, a left shift in the peripheral blood count at the time of diagnosis of acute lymphocytic leukemia has been correlated with duration of complete remission 2. The presence of these immature cells reflects the normal maturation sequence of granulocytes, where myeloblasts develop into promyelocytes, then myelocytes, metamyelocytes, band cells, and finally mature neutrophils. When demand exceeds supply of mature cells, earlier forms enter circulation.
Some studies have investigated the development and fate of neutrophil giant metamyelocytes, suggesting that they result from an abnormal type of development in promyelocytes and myelocytes which have been arrested or retarded in their progress through the cell cycle 3. However, the most recent and relevant study to this question is not directly related to the development of metamyelocytes, but rather to the use of liquid biopsies in multiple myeloma patients, highlighting the importance of precision medicine approaches in hematological malignancies 4.
Key points to consider in the presence of metamyelocytes and myelocytes in the blood include:
- The need for further investigation, including complete blood count with differential and bone marrow examination if appropriate
- The potential causes, including acute infection or inflammation, leukemia, myeloproliferative disorders, myelodysplastic syndromes, or bone marrow infiltration by cancer
- The importance of considering the quantity of immature cells and the patient's overall clinical picture in determining the severity and clinical significance of the finding.