Neutropenia is the decrease to the normal Neutrophil count. Neutropenia is defined as the Neutrophil count that less than 2,500 cells/µL.

The normal white blood cell count for the Neutrophil is 8870 segmental (mature) cells/µL in newborns which drops down dramatically within 2 weeks to lower than 2600 cells/µL, then the normal Neutrophil count starts to increase again to reach 3800 cells/µL in adults.

Since the Neutrophil makes up the majority of white blood cells, except at early childhood, a massive decrease in the Neutrophils count (severe Neutropenia) would cause a noticeable decrease in the total blood cells count (Leukopenia) and sometimes the terms Neutropenia and Leukopenia may be used to refer to each other. But Neutropenia is just a subtype of Leukopenia.

Neutrophils are decreased in the circulating blood by exposure to radiation and Neutropenia is considered as a side effect to Radiation Therapy.

Anaphylactic reaction (Anaphylaxis) is another cause of Neutropenia. Anaphylaxis occurs when the whole body is reacting to an exposure of a chemical that the body is allergic to.

Systemic lupus erythematosus (SLE) is an immune system disease that defines the situation when white blood cells are mistakenly attack the non-harmful body tissues. Neutropenia is a significant sign in this because the Neutrophils are attacking a massive number of cells that builds up the non-harmful tissue (Same mechanism that causes Leukopenia in overwhelming infections).

The infections listed below decrease the production of Neutrophil and Neutropenia can be a sign of any of them:

  • Brucellosis.
  • Measles.
  • Infectious Mononucleosis Malaria .
  • Tuberculosis.
  •  Typhoid Fever.
  •  Tularemia.
  •  Viral Hepatitis.

Neutropenia is also associated to chemical therapy because the Neutrophil production is reduced by several drugs including:

  • Antiinflamatory gents that treat inflammation by altering the activation and migration of Neutrophil.
  • Alkylating agents including Busulfan, Chlormbucil, Cyclophosphatmide, and Nitrogen mustard.
  • Antimetabolites (Drugs that block the cell growth and cell division) including Methotrexate, 5-fluorocyosine, 6-mercaptopurine and the Antimetabolite Antibiotics such like Penicillin and the Sulfonamides.
  • Antithyroid agents.

There are drugs that destroy the Neutrophil in the blood causing Neutropenia including Aminopyrine, Methyldopa, Phenylbutazone, and Mecurial Diuretics.