blood processing systems and methods establish on line communication between a container and a source of blood containing leukocytes and platelets , such as a human donor . the systems and methods create a centrifugal field between the source of blood and the container that separates from the blood an unfinished suspension of platelets having a first physiologic characteristic different than the desired physiologic characteristic . the systems and methods pump the unfinished platelet suspension outside the centrifugal field through a finishing device . the finishing device changes the first physiologic characteristic to the desired physiological characteristic , thereby creating the finished platelet suspension . the systems and methods convey the finished platelet suspension from the finishing device directly into the container . the systems and methods function without interrupting the on line communication between the container and the source of blood .