Neutrophils are one of the first lines of host defense against invading pathogens, particularly bacteria. The most important sequela of severe neutropenia is increased susceptibility to infection, often by organisms in the normal flora of the gastrointestinal tract, nasopharynx, and skin. Neutropenia can be caused by decreased bone marrow production or increased use of neutrophils beyond the rate of marrow production or it can be secondary to immune-mediated processes that suppress marrow granulopoiesis or destroy circulating neutrophils. The underlying disease process determines clinical outcome in most circumstances.
