Neutrophil production and kinetics: Neutropenia and neutrophilia

Changes in neutrophil count are frequently encountered in clinical medicine in that increased or decreased neutrophil counts are often seen with infections and other disorders. This chapter focuses on neutrophil kinetics and common reasons for aberration, and deals with esoteric disorders that primarily affect myeloid cells. Neutrophils must cross the vascular wall to get to sites of inflammation, a process referred to as diapedesis. Neutrophils may extend their antimicrobial activity, beyond phagocytosis and degranulation, and beyond their lifespan, by forming neutrophil extracellular traps. Neutrophilias are acquired disorders, most commonly reactive phenomena with only a small minority representing a primary hematologic disorder. The evaluation of neutrophilic leukocytosis begins with a history focused on potential causative factors, particularly infections. In the hospital, the most common causes of neutropenia are medication reactions or sepsis, and these become especially suspect if the neutropenia has its initial onset during hospitalization.