What explains the presence of metamyelocytes after a bone marrow transplant (BMT)?

The presence of metamyelocytes after a bone marrow transplant is typically a normal finding that indicates engraftment and recovery of the bone marrow. Metamyelocytes are immature white blood cells that represent an intermediate stage in the development of neutrophils. Following a bone marrow transplant, the donor stem cells begin to establish themselves and produce new blood cells in a process called engraftment. During this recovery phase, it's common to see various immature cell forms, including metamyelocytes, in the peripheral blood. This finding usually appears around 10-28 days post-transplant and represents a positive sign that the new marrow is functioning. The appearance of these cells often precedes full neutrophil recovery and suggests that the patient is moving toward normal hematopoiesis. If metamyelocytes persist in large numbers beyond the expected engraftment period or appear alongside other abnormal cells, further evaluation may be warranted to rule out complications such as infection, graft-versus-host disease, or relapse of the original disease. Regular complete blood counts with differential are typically performed to monitor this process during post-transplant recovery.