The normal level of neutrophils in human blood varies slightly by age and race. Infants have lower counts than older children and adults, and African Americans have lower counts than Caucasians or Asians. The average adult level is 1500 cells/mm3 of blood. Neutrophil counts (in cells/mm3) are interpreted as follows:

• greater than 1000. Normal protection against infection.
• 500–1000. Some increased risk of infection.
• 200–500. Great risk of severe infection.
• lower than 200. Risk of overwhelming infection; requires hospital treatment with antibiotics.

Neutropenia may result from three processes:

Lowered production of white blood cells is the most common cause of neutropenia. It can result from:

• medications that affect the bone marrow, including cancer drugs, chloramphenicol (Chloromycetin), anticonvulsant medications, and antipsychotic drugs (Thorazine, Prolixin, and other phenothiazines)
• hereditary and congenital disorders that affect the bone marrow, including familial neutropenia, cyclic neutropenia, and infantile agranulocytosis
• cancer, including certain types of leukemia
• radiation therapy
• exposure to pesticides
• vitamin B12 and folate (folic acid) deficiency

WBCs are used up at a faster rate by:

• acute bacterial infections in adults
• infections in newborns
• certain autoimmune disorders, including systemic lupus erythematosus (SLE)
• penicillin, phenytoin (Dilantin), and sulfonamide medications (Benemid, Bactrim, Gantanol)

Sequestration and margination are processes in which neutrophils are removed from the general blood circulation and redistributed within the body. These processes can occur because of:

• hemodialysis
• felty's syndrome or malaria, the neutrophils accumulate in the spleen
• bacterial infections, the neutrophils remain in the infected tissues without returning to the bloodstream

Neutropenia has no specific symptoms except the severity of the patient's current infection. In severe neutropenia, the patient is likely to develop periodontal disease, oral and rectal ulcers, fever, and bacterial pneumonia. Fever recurring every 19–30 days suggests cyclical neutropenia.

Diagnosis is made on the basis of a white blood cell count and differential. The cause of neutropenia is often difficult to establish and depends on a combination of the patient's history, genetic evaluation, bone marrow biopsy, and repeated measurements of the WBC.

Treatment of neutropenia depends on the underlying cause.

Patients with fever and other signs of infection are treated for seven to 10 days with antibiotics. Nutritional deficiencies are corrected by green vegetables to supply folic acid, and by vitamin B supplements.

Medications known to cause neutropenia are stopped. Neutropenia related to pesticide exposure is treated by removing the patient from the contaminated environment.

Patients receiving chemotherapy for cancer may be given a blood growth factor called sargramostim (Leukine, Prokine) to stimulate WBC production.

Patients with Felty's syndrome who have repeated infections may have their spleens removed.

The prognosis for mild or chronic neutropenia is excellent. Recovery from acute neutropenia depends on the severity of the patient's infection and the promptness of treatment.