The term "leukemoid reaction" is used to describe a condition where peripheral white blood cells on a stained blood smear may have some resemblance to leukemia cells. Quantatively, in a leukemoid reaction, the neutrophil count may be as high as 50.0 X 109/L with more immature cells, particularly myelocytes, than are usually present in toxic left-shift syndromes.
The presence of immature cells in a leukemoid reaction awakens thoughts of leukemia. Great care must be taken to make a distinct differentiation between aberrant white blood cell proliferations (possible leukemia) and a benign but exaggerated granulocytic proliferative response (leukemoid reaction). The leukocyte alkaline phosphatase (LAP) score is low in myelocytic leukemia and high in leukemoid reaction.
This particular peripheral smear represents a leukemoid reaction.
