Neutrophils are a type of white blood cell. Like other white blood cells in you or your child’s immune system, neutrophils play an important role in fighting infection. Patients who have too few neutrophils, known as neutropenia, are at risk for both recurrent and severe infections, especially bacterial and fungal infections.

Neutropenia may be present at birth or develop later in life. Some cases of neutropenia are due to an underlying inherited genetic condition, while other cases of neutropenia are due to an acquired cause such as viral or drug/toxin exposures. In some cases of neutropenia, the underlying cause cannot be identified and the term "idiopathic" is used.

Historically, the management and treatment options for patients with neutropenia were limited to antibiotics. However, since the advent and approval of granulocyte colony stimulating factor (G-CSF) in the 1990s, G-CSF has played a major role in the management of patients with neutropenia. G-CSF is an injectable medication that stimulates the patient’s bone marrow to make more neutrophils, thereby helping to raise the neutrophil count and decrease infection risk. Not all patients will respond to G-CSF and other treatment modalities such as bone marrow transplantation are sometimes necessary.

Problems with infection can also arise if the neutrophils are present in normal numbers but do not function properly. In order to effectively kill bacteria and fungus, neutrophils have to accomplish a number of activities effectively, including: maturation in the bone marrow, traveling in the blood stream and exiting at the site of active infection, recognition of the infectious organism and killing the foreign pathogen by ingestion. If any of these steps are disrupted, the neutrophil is not able to function normally and the person will be susceptible to infection. Treatment of functional neutrophil disorders, such as chronic granulomatous disease, requires specialized care often from many specialists and patients benefit greatly from being cared for in a multidisciplinary setting.