Figure 2 Bone marrow biopsy in Patient A. Under 4× magnification (A), a high cell density was observed, with prominent granulocytic proliferation – predominantly neutrophils – indicating active myeloid hyperplasia. The remaining images at 40× magnification (B–D) reveal an increased number of segmented neutrophils (red arrows), some exhibiting vacuolation (blue arrows), along with metamyelocytes (green arrows) and promyelocytes (black arrows). Overall, the bone marrow demonstrated active hematopoiesis with marked proliferation of segmented and immature granulocytes, without any abnormal increase in blasts or nuclear atypia. Key diagnostic features of a leukemoid reaction include a markedly elevated neutrophil count and reduced but morphologically normal erythroid lineage cells, in contrast to leukemia, which typically shows a high proportion of blasts and aberrant nuclear chromatin. The annotations showing segmented neutrophils, neutrophil vacuolation, and immature granulocytes clearly illustrate microscopic hallmarks of a leukemoid reaction, supporting the clinical diagnosis.