Schematic view of neutrophil kinetics. Neutrophil kinetics divides into 3 phases: marrow, blood, and tissues. In the marrow, developing neutrophils spend about half their time in the mitotic pool as myeloblasts, promyelocytes, myelocytes. The time to transit this pool is the mitotic pool transit time (MPPT). They then enter the postmitotic pool, becoming sequentially metamyelocytes, bands, and then neutrophils. The time for the neutrophil to pass through these stages is referred to as the postmitotic pool transit time (PMPTT). Neutrophils in the circulation are about equally divided between the circulating and marginal pools. Neutrophils leave the circulation and enter the tissues at inflammatory sites or become effete cells and are removed by macrophages in the spleen, marrow, and other tissues.