Neutrophils are the most numerous type of leucocyte, constituting approximately 65% of circulating white cells. About 50% of neutrophils marginate to the blood vessel walls and are not counted in the FBC. They demarginate in response to infection, exercise or corticosteroid therapy and have a life span of about 10 hours.
Neutrophils are differentiated from other leucocytes by Side Fluorescent Light and Forward Scattered Light measurements in the Sysmex XN WDF Channel.
If immature neutrophils are seen on a blood film, the number of myeloblasts, promyelocytes, myelocytes and metamyelocytes are counted as part of a 100 white cell differential. The number of promyelocytes, myelocytes and metamyelocytes are counted together in the absolute immature granulocyte count. Mature neutrophils have a purple staining nucleus in Romanovsky stained slides, containing 2-5 lobes. The pale pink cytoplasm contains many fine purple staining granules.
Neutrophil Function
Neutrophils are attracted to micro-organisms or sites of inflammation due to the release of chemotactic substances. Phagocytosis then occurs and the micro-organism is surrounded by membrane and fused with a primary lysosome. This phagosome is then attacked by bactericidal proteins and hydrolytic enzymes contained in the primary and secondary granules, as well as hydrogen peroxide. Neutrophils also have a major immunomodulatory role, releasing many cytokines in response to stimulation.
Causes of a raised neutrophil count (neutrophilia):
Physiologic - Stress, labour, neonate, exercise, seizure.
Infection - Bacterial.
Inflammation - Myositis, vasculitis, dermatitis, trauma, tumour necrosis.
Drugs - Steroids, epinephrine, digitalis, G-CSF, GM-CSF.
Metabolic disorders - Uraemia, acidosis, gout, eclampsia.
Haematologic - Acute haemorrhage or haemolysis, myeloproliferative disorders, idiopathic.
Causes of a reduced neutrophil count (neutropenia):
Severe infection - Bacterial (especially gram negative), viral (EBV, HIV, hepatitis), protozoal.
Drugs
Irradiation
Immune - Idiopathic, Felty's syndrome, maternal iso-antibodies, SLE.
Hypersplenism
Congenital - Kostman's syndrome
Cyclical neutropenia
Marrow aplasia - PNH, aplastic anaemia.
Marrow infiltration - Myeloproliferative disorders, leukaemia.
Megaloblastic anaemia.