In a normal peripheral blood smear, there are relatively few white blood cells. Green arrows mark neutrophils (PMNs) and yellow marks a lymphocyte.
In acute inflammation (such as bacterial infections) there is an increase in the neutrophil count in peripheral blood. Since the body is in a hurry to release these PMNs, they have not all completely matured into the multi-lobed nuclei. This phenomenom is called a "left shift."
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Cancer of the bone marrow causes an increase in the numbers of leukocytes in the peripheral blood. How do you distinguish this from simple inflammation? Notice that all of the stages of the maturing white cells are present rather than just the mature (or nearly mature) forms.
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