Neutropenia is defined as an absolute neutrophil count (ANC) of less than 1500 per microliter (1500/microL). Severe neutropenia is defined as less than 500 per microliter (500/microL). The causes of primary defects of neutrophil function include failure of the following: Adhere to endothelial cells, Migrate into inflammation sites (abnormal chemotaxis), Ingest and kill bacteria, Produce microbicidal compounds to kill fungi and other pathogens, Form phagolysosomes, Make high concentrations of tox