White blood cells, also known as leucocytes, are cells found in the blood, and they form an important part of the body's immune system. White blood cells help protect against infections and play a part in inflammatory and allergic reactions. The number of white blood cells indicates the concentration of white blood cells in a blood sample. This is a test that is part of a full blood count, which is often used in a general assessment of the health of an individual.
When there is an infection or an inflammatory process somewhere in the body, the bone marrow produces more white blood cells and releases them into the blood where a complex process moves the cells to the site of infection or inflammation. As soon as the infection or inflammation has diminished, the production of white blood cells in the bone marrow will decrease and the number of white blood cells returns to normal levels.
White blood cells are analysed in order to find out the concentration of white blood cells. Besides infections and inflammations, a number of other factors can influence the production of white blood cells in the bone marrow and the survival of white blood cells in the blood. These factors may include cancer or autoimmune disorders, resulting in either an increase or a decrease in the number of white blood cells in the blood. The number of white blood cells – together with the other components in a full blood count – can indicate potential health problems.
If the results indicate a problem, a broad range of other tests are available that ought to be carried out in order to help determine the cause.
Seen in chronic inflammatory processes, myeloproliferative syndrome, thrombocyte function defects, splenectomy.
Seen in reduced bone marrow production in cases of aplastic anaemia, leukaemia, myelosuppressive substances, shortage of vitamin B and folate, and in cases of increased consumption of autoantibodies, infection, haemolytic states, SLE, splenomegaly, decimated intravascular coagulation (DIC). Thrombocyte aggregates in the EDTA tube can give a falsely low thrombocyte count.