White Blood Cells (WBC, Leukocytes, Leukocyte Count, White Count)
Leukocytes are colorless blood cells that have nuclei. They are produced in the bone marrow and lymph nodes. Their main function is protecting the body against microbes, bacteria, viruses and foreign cells. White blood cells produce antibodies, are engaged in immune reactions, and bind and destroy harmful agents.
Leukocytosis (elevated levels of white blood cells) indicates an inflammatory process or acute infections – mostly bacterial ones. A high white blood cell count is not always an indicator of some disease – white blood cells respond to various changes in the body. For instance, stress, pregnancy or exercise may cause an increase in white blood cell counts.
A low white blood cell count (leukopenia) is an indicator of a weakened immune system. Leukopenia may be caused by some viral infections, such as flu, chicken pox, and German measles, or medications, such as analgesics or anticonvulsant drugs.
All white blood cells are divided into five types: neutrophils, eosinophils, basophils, lymphocytes, and monocytes, and each has their own function. The percentage of one of the five types of leukocytes falls or rises due to a decrease or increase in the other types of leukocytes. For instance, a white blood count may show the type of leukocytes due to which an increase in total leukocytes occurs. A white blood count may be indicative of complications and pathological processes, as well as help forecast the clinical outcome.
It is important to understand the difference between relative and absolute changes in different types of leukocytes in the blood. A relative change in white blood counts means that the percentage of certain types of leukocytes is higher or lower than normal. Apart from the percentage ratio of leukocytes, their absolute values are also calculated, meaning how many cells of each type of leukocytes are contained in one liter of blood.
Below is a formula to calculate the absolute value of each type of leukocytes per one volume of blood:
А(%) x WBC(109/L)/100,
А (%) – share of the specific type of leukocytes as compared with the other leukocytes in %,
WBC (109/L) – white blood cell count.
For example, a white blood count shows 12% of lymphocytes which is significantly lower than normal levels. If the total number of leukocytes is 13,0 х 109 cells/L, the absolute value of lymphocytes will be 1,56 х 109 cells/L which is within the normal range.
Remember that absolute values are not only more informative than relative ones. They are the only values showing the objective blood picture, while relative values are intermediate, needed to calculate the absolute values, and are not independent.
During pregnancy, a slightly elevated white blood cell count is a physiological response to the stimulation of blood formation and requires no treatment.