Neutropenia is a disorder of the circulatory system. It occurs when someone's nuetrophil granulocyte count becomes inordinately low. A type of white blood cell, nuetrophil granulocytes usually constitute about fifty to seventy percent of white blood cells in the circulatory system. These act as a first line of defense against invading bacteria. When nuetropenia occurs, the body becomes susceptible to these invading pathogens. Symptoms of the disease include fever, mouth ulcers, diarrhea, chills, shortness of breath, and a sore throat.

It is usually agreed that there are four classifications of neutropenia. This is done by measuring what is called the "absolute neutropenia count," or ANC. If a microliter of blood contains less than two thousand counts, it is termed general neutropenia. With this condition, there is an above average chance of acquiring an infection due to decreased white blood cells. This is the least severe of the classifications. Mild neutropenia occurs when the ANC count drops below the fifteen hundred level, and yet is above the one thousand count mark. Moderate neutropenia occurs between one thousand and five hundred ANC, and severe neutropenia is marked by any ANC below five hundred. If one is diagnosed with severe neutropenia, there is a good chance that they are in danger of an imminent infection.

There are five main types of the latter kind of neutropenia, the most severe form. The first is congenital neutropenia. This type occurs at birth. It is one of the rarest types and can be one of the most difficult to deal with. This condition can cause bone deterioration, tooth loss, and gum erosion. The second type of the disease is the cyclical variety. It occurs in phases, usually once every three weeks. It lasts from three to six days per occurrence. When this condition occurs, it is not uncommon for it to be shared among several members of one family. Its severity usually subsides somewhat after puberty.

Idiopathic neutropenia usually develops during or shortly after another illness. It seems that when a gateway opens and an opportunity presents itself, this condition takes advantage of it and secures a place for itself with the body. Autoimmune neutropenia is characterized by the body, essentially, fighting itself; neutrophils are identified as foreign enemies and the body works to destroy them. Neutropenia can also be induced by artificial, chemical means. Drugs introduced into the body can act to completely eliminate the body's white blood cells, creating a dangerous environment in which bacteria can thrive.