A peripheral blood picture resembling that of leukemia or indistinguishable from it on the basis of morphologic appearance alone. (dorland, 27th ed)

The term leukemoid reaction describes an increased white blood cell count (> 50,000 cells/μL), which is a physiological response to stress or infection (as opposed to a primary blood malignancy, such as leukemia). It often describes the presence of immature cells such as myeloblasts or red blood cells with nuclei in the peripheral blood. It may be lymphoid or myeloid..