This is something your GP may talk to you about after reviewing your blood tests. It sounds very scary but the vast majority of times there is usually a very simple and non-worrying reason.

White cells are blood cells that circulate around our body in the blood stream, but are also found within our tissues and organs. They are the body’s natural security guards for patrolling around the body, identifying and fighting unwanted invaders such as bacterial and viral infections. They are also pivotal in participating in and controlling inflammation.

There are two main types. Leukocytes (polymorpholeukocytes or PMLs) and lymphocytes (which include monocytes).


Leukocytes come in 3 forms, basophils (immediately forget!), eosinophils (which are usually involved in allergic type reactions such as asthma, hay fever and eczema) and neutrophils. They get these names because of the way they stain in the laboratory when scientists want to examine them under the microscope.

All these cells have ‘normal’ ranges in the blood stream which are pretty consistent. There may be genetic and ethnic variation in these counts (for example, African-Carribbean patients often have lower levels of neutrophils).

The most important cells of the leukocyte group are the neutrophils and it is these cells that the comprise the largest portion of the white cells by far. They are mainly responsible for fighting bacterial infections. When a bacterial infection occurs, chemical signals are released by damaged tissue and other cells near the infection, which alert neutrophils to the problem. As a result several things happen;

  • more neutrophils enter the blood stream (white cell count goes up)

  • neutrophils invade the area to fight the infection

  • more chemicals are released to prime the immune system

  • other chemicals are released to increase the body temperature (this has the effect of significantly improving the performance of the neutrophils)

The neutrophils kill bacteria by engulfing them and killing them with chemicals that they produce.

Lymphocytes (and monocytes)

These cells are also found in the blood stream and tissues, but tend to congregate in the spleen and the lymph glands which are found all over the body. Lymphocytes are mainly responsible for fighting viral infections.

They get recruited into areas of viral attack in the same way that neutrophils do but deal with them in a slightly different way. They produce a lot of different types of signal chemicals that

stimulate the immune system to produce antibodies and other attack proteins to neutralise viral infections.

Both neutrophils and lymphocytes are involved in inflammation and chronic inflammatory conditions (such as rheumatoid arthritis or inflammatory bowel disease) where there is no obvious infection and frequently the cause of these conditions is not well understood.

Causes of high white cell count

  • Infection (commonest by far)

  • Inflammation

  • reaction to cancer (rare)

  • Blood disorders (such as polycythaemia and rarely, leukaemia)

Causes of low white cell count

  • ethnic

  • reduced bone marrow production (marrow failure, myelofibrosis, myelodysplasia)

  • overwhelming infection (white cells get used up and the bone marrow reduces output)

  • certain drugs (in particular following chemotherapy)


Dr Helen Webberley

Dr Helen Webberley is an NHS GP with a practice in South Wales, and an experienced online doctor providing healthcare advice and treatment via the Internet. She is a talkhealth expert in the Online Clinics. If anyone has any queries about their health then feel free to contact her.

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