Neutropenia (cont.)

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What is neutropenia?

Neutropenia is a condition in which the number of neutrophils in the bloodstream is decreased. Neutrophils are a type of white blood cell also known as polymorphonuclear leukocytes or PMNs. Neutropenia reduces the body's ability to fight off bacterial infections.

White blood cells are also known as leukocytes. There are five major types of circulating white blood cells:

  1. basophils,
  2. eosinophils,
  3. lymphocytes (T-cells and B-cells,
  4. monocytes, and
  5. neutrophils.

Some white blood cells, called granulocytes, are filled with microscopic granules that are little sacs containing enzymes (compounds that digest microorganisms). Neutrophils, eosinophils, and basophils are all granulocytes and are part of the innate immune system with somewhat nonspecific, broad-based activity. They do not respond exclusively to specific antigens, as do the lymphocytes (B-cells and T-cells).

Neutrophils contain enzymes that help the cell kill and digest microorganisms it has engulfed by a process known as phagocytosis. The mature neutrophil has a segmented nucleus (it is often called a 'seg' or 'poly'), while the immature neutrophil has a band-shape nucleus (it is called a band). Neutrophils are made in the bone marrow and released into the bloodstream. The neutrophil has a life-span of about three days.

How is neutropenia defined?

The white blood cell count (WBC) is the number of white blood cells in a volume of blood. The normal range for the WBC varies slightly among laboratories but is generally between 4,300 and 10,800 cells per microliter or cubic millimeter (cmm). The WBC can also be referred to as the leukocyte count and can be expressed in international units as 4.3 x 109to 10.8 x 109 cells per liter. The percentage of the different types of white blood cells in the WBC is called the WBC differential.

The absolute neutrophil count (ANC) is determined by the product of the white blood cell count (WBC) and the fraction of neutrophils among the white blood cells as determined by the WBC differential analysis. For example, if the WBC is 10,000 per microliter and 70% are neutrophils, the ANC would be 7,000 per microliter.

An ANC of less than 1500 per microliter (1500/microL) is the generally accepted definition of neutropenia. Neutropenia is sometimes further classified as:

  • mild if the ANC ranges from 1000-1500/microL,
  • moderate with an ANC of 500-1000/microL, and
  • severe if the ANC is below 500/microL.

Some medical terms may be used synonymously with neutropenia, even though their precise definitions are different.

  • Leukopenia refers to a reduced number of white blood cells in general, while granulocytopenia refers to a decreased number of all the granulocyte-type blood cells (neutrophils, eosinophils, and basophils).
  • Since neutrophils normally far outnumber the other types of granulocytes, this term is sometimes used to refer to neutropenia.
  • Finally, agranulocytosis literally refers to a complete absence of all granulocytes, but this term is sometimes used to refer to severe neutropenia.
Medically Reviewed by a Doctor on 12/4/2013

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