The role of white blood cells is to engulf and destroy invading germs, and to provide immunity. There are many reasons why the number of white blood cells might fall.
Certain viruses such as HIV, autoimmune diseases, and cancers such as leukaemia can all affect white blood cell count.
There are also medicines and treatments, including radiation therapy and chemotherapy used in cancer treatment that can affect bone marrow and cause neutropenia - the condition of having too few white blood cells. A comprehensive list of causes can be found on the Mayo Clinic’s website.
There are five different types of leucocytes, (also spelled leukocytes), or white blood cells, and they are all made in stem cells in the marrow of bones. The leucocytes leave the bone marrow, enter the blood and spread throughout the body.
Doctors are usually interested in the WBC count because when the numbers rise, they often indicate that there is an infection in the body, and when they fall, this could be indicative of some of problems listed above. If repeat blood tests show that the white blood cell count stays low, further investigation is called for.
When dealing with abnormal lab results, it is important to remember that the numbers need to be put into context. Questions need to be asked about whether there are other symptoms, before any firm conclusions can be drawn about what a low white blood cell count actually means.