Neutrophils are the most abundant leukocyte, comprising 50-70% of all white blood cells and are a critical component of the immune system. Immature neutrophils have a distinct band-shaped nucleus which changes into a segmented nucleus following maturation. Normally located in the circulating blood system, neutrophils migrate to sites of infection via chemotaxis directed by molecules such as Leukotriene B4. The main function of neutrophils is to destroy micro-organisms and foreign particles by phagocytosis. The number of circulating neutrophils is estimated using the absolute neutrophil count (ANC). An ANC may be high due to kidney failure or eclamspia. In contrast, leukemia and bone marrow damage result in a lower number of neutrophils (neutropenia) and an increased risk of infection.