Neutrophilic granulocytes are usually circular and have a light-grey to pink cytoplasm. The diameter is usually around 14 µm. The granules are very fine and range in color from reddish-violet to brown. The nucleus of band neutrophils is bent and oblong partly with constrictions which have not yet resulted in a filament.
The neutrophil count usually is between and x 109/L. The deviation from this normal range downwards is known as neutropenia and upwards as neutrophilia. If the neutrophil count falls to under 0.5 x 109/L, severe neutropenia is present. This condition can be life threatening since it can lead to severe infections.
One of the main tasks of neutrophils is defense against bacterial infections, by phagocytizing the pathogens and killing them. Neutrophils can leave the bloodstream and move into the surrounding tissue, to fight infection (see video on motility of neutrophils). Normally, they remain in the blood stream for about six hours and in the surrounding tissue for 1-2 days. About half of the neutrophils do not circulate in the peripheral blood, but rather adhere to the walls of smaller vessels (marginal pool).
Neutrophilic granulocytes can be subdivided by means of their nuclear structure into band neutrophils and segmented neutrophils. There are two different definitions which explain this subdivision.
Definition #1: As soon as the nucleus is threadlike and constricted at any given place, it can be called a segmented neutrophil. Before that it is called a band neutrophil (The rule of filament).
Definition #2: As soon as the diameter of the nucleus at any given place is less than 1/3 that of its widest point, it is a segmented neutrophil (The rule of one third).
Subsequently, different normal values result depending on which definition is used.
Band cells are younger than segmented cells. Neutrophils with more than four constrictions are regarded as hypersegmented. The ratio of band neutrophils to segmented neutrophils is normally around 1 to 4 (the rule of filament), respectively 1 to 12-15 (the rule of one third). If the ratio shifts and there are more band neutrophils, it is called shift to the left or immaturity.
The normal range of band neutrophils is 0.1 to 1.8 x 109/L, that of segmented neutrophils 1.3 to 7.0 x 109/L. According to the rule of filament, this represents 3 to 17% band neutrophils and/or 37 to 67% segmented neutrophils.
Neutrophilia can have various causes. Mobilization of the marginal pool is typical in stressful situations (stress induced leukocytosis). Acute infections and inflammation result in the mobilization of neutrophils from bone marrow. Younger forms are prevalent, which is referred to as shift to the left. In addition, toxic alteration can arise especially in cases of bacterial infections. Neutrophilia accompanied by the release of immature preliminary stages is called a leukemoid reaction. This must be distinguished from chronic myelocytic leukemia, where additional eosinophilia, basophilia and splenomegaly are typically present. Chronic infections and inflammation processes may lead to chronically elevated neutrophil counts.
Neutropenia can be caused by reduced production of or increased consumption of neutrophils. Causes of selective neutropenia can include medications (e.g. non steroidal anti-inflammatory drugs), infections (e.g. typhoid fever, malaria, various viral infections) or autoimmune diseases (e.g. systemic lupus erythematosus). Neutropenia accompanied by anemia and/or thrombocytopenia occurs in cases of acquired bone marrow failure, leukemias, megaloblastic anemia as well as chemotherapy. Splenomegaly (Hypersplenism) can be an additional cause. Neutropenia can be accompanied by an increased susceptibility to infections. This is especially true if the neutrophil count falls to under 0.5 x 109/L (severe neutropenia).
Hyper segmentation of neutrophils is usually a sign of vitamin B12 or folic acid deficiency (megaloblastic anemia).