White blood cells, also known as leukocytes, account for less than 1% of your blood cells, but are very important for health and protection against disease. These are the cells that defend the body against viruses and bacteria. Having a low or elevated white blood cell count can indicate a range of disorders relating to the blood and bone marrow.
A low white blood cell count is also sometimes called leukopenia (or leukocytopenia). White blood cell count varies from person to person.
The normal range is usually between 4,000 and 11,000 white blood cells per microliter of blood. Anything below 4,000 is typically considered to be a low white blood cell count.
Low white blood cell count is often caused by problems with the bone marrow where they are made. The bone marrow is the spongy tissue inside of bones which is responsible for creating most of the body’s blood cells.
Certain types of cancer, such as leukemia, and treatments such as chemotherapy can damage the bone marrow’s ability to create white blood cells. Chemicals such as benzene and certain pesticides can also damage the bone marrow.
Another common cause for a low white blood cell count is infection. An infection can affect the bone marrow and make it difficult for the body to produce white blood cells. Also, when the body is fighting a particularly severe infection, the rate of white cell production, even when stepped up in response, may not keep up with the rate at which white blood cells are being used up in combating the disease.
Other causes of leukopenia include autoimmune disorders, such as lupus and rheumatoid arthritis, which cause the body to attack its own white blood cells. Certain medications can also destroy white blood cells. Vitamin deficiency, excessive alcohol consumption and generally poor diet can also lower a white blood cell count.
Abnormally low white blood cell levels could lead to higher risk of infection of any kind. A low white cell count itself does not directly produce any symptoms, but a patient who is immunocompromised as the result of significant leukopenia and then develops an infection may experience symptoms associated with that infection, such as fever, localized pain, fatigue, muscle ache, loss of appetite and general malaise.
The main risk of an abnormally low white blood cell count is how vulnerable it may make a person to infection. Without an adequate white blood cell response available to fight infection, the body is at greater risk that any infection (including those usually regarded as minor) may cause serious illness or death.
Risk of infection is an even greater concern for a patient whose immunity is already compromised for some reason. One example of this is a low neutrophil count (neutrophils are a type of white blood cell involved in fighting bacterial infection) caused by the effect of cancer chemotherapy on the bone marrow. Where this is the case, treatments may need to be rescheduled to allow recovery of the white cell count and medications may be given to stimulate the growth of neutrophils to help maintain adequate levels.
Since leukopenia is itself asymptomatic and chronic infection may go unrecognised because of failure to mount a symptomatic response, immunocompromised patients will usually have a periodic blood count to monitor their white cell count along with other regular health checks.
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