The presence of abnormally small numbers of neutrophils (mature white blood cells) in the circulating blood of the body.

Neutrophils are white blood cells (WBCs) produced in the bone marrow that ingest bacteria. Neutropenia is sometimes called agranulocytosis or granulocytopenia because neutrophils make up about 60% of white blood cells and have granules inside their cell walls.

Neutropenia is a serious disorder because it makes the body vulnerable to bacterial and fungal infections.

The normal level of neutrophils in human blood varies slightly according to age and race. Infants have lower counts than older children and adults, and African Americans tend to have lower counts than Caucasians or Asians.