What are leukocytes?
Leukocytes are blood cells that, unlike red blood cells (erythrocytes), do not contain red blood pigment. They therefore appear “white” or colorless. They are therefore also called white blood cells.
The main task of leukocytes is to defend the body against pathogens. White blood cells are found in the blood, tissues, mucous membranes and lymph nodes. Many of them have the ability to actively move around and can migrate into tissues from blood vessels.
All leukocytes are derived from a common bone marrow progenitor cell called a pluripotent stem cell. Special growth factors ensure that the stem cell develops into the various white blood cells: Granulocytes, Monocytes and Lymphocytes.
Granulocytes
Granulocytes show a “granular” appearance inside under the microscope. Depending on the stainability of the cell components, a distinction is made under the microscope between basophilic, neutrophilic and eosinophilic granulocytes. Each of these cell types takes care of different pathogen forms and proceeds differently in the defense against infection.
Since granulocytes can move on their own, they can migrate out of the blood vessel into the tissue and mucous membranes. After four to five days, granulocytes that migrate to tissues are also degraded.
Monocytes
Monocytes have the task of taking up foreign material (phagocytizing) and making it harmless. Therefore, such blood cells are also called phagocytes. A large part of monocytes is stored in the spleen, another part circulates in the blood.
Lymphocytes
Lymphocytes are highly important cells in immune defense. They recognize hostile pathogens such as bacteria or viruses and produce antibodies against them. In this way, the pathogens can be inactivated and destroyed. Some lymphocytes, so-called memory cells, can “remember” the nature of the pathogens. They form the body’s own immune protection and ensure that one can contract certain diseases only once in a lifetime or only at longer intervals. The life span of lymphocytes ranges from a few hours to several years.
When to determine the leukocyte value?
The physician has the leukocyte values determined in the following cases:
- Suspected infections and inflammations
- Blood anemia (anemia)
- Suspicion of leukemia or myeloproliferative neoplasia (too many cells are then produced in the bone marrow that are not fully functional)
- before and after radiotherapy or chemotherapy
- with certain drug therapies
- after infarctions or burns
- after poisoning
- to control the course of disease in connective tissue diseases (collagenoses) and autoimmune diseases
Normally it is sufficient to determine the number of total leukocytes. Sometimes, however, it is necessary to differentiate more precisely how many leukocytes of which type are present. This is called differential blood count. It is performed, for example, in the case of severe infections, persistent fever or blood cancer.
The leukocyte count is determined in the urine to diagnose a urinary tract infection. For this purpose, the white blood cells found in the urine can also be counted under the microscope. This is then referred to as cell count per field of view.
Leukocyte normal values
|
Blood values Leukocytes |
Leukocytes in urine sediment |
|
|
Leukocyte standard value |
4.000 – 10.000 cells/µl |
0 – 3 cells/µl or <5 cells/field of view (under microscope) |
The following standard values apply to the exact breakdown of leukocytes in the differential blood count:
|
Differential blood count |
Blood values leukocytes |
|
Granulocytes |
a) rod-nucleated neutrophil G.: 3 – 5 %. b) segment-nucleated neutrophilic G.: 50 – 70 %. Eosinophilic granulocytes: 1 – 4 % basophilic granulocytes: 0 – 1 % |
|
Monocytes |
3 – 7 % |
|
Lymphocytes |
25 – 45 % |
When are there too few leukocytes in the blood?
If there are too few leukocytes in the blood, this is called leukopenia or leukocytopenia. Often the number of granulocytes is reduced, while the number of the remaining leukocytes is within the normal range.
Read more about possible causes of low leukocyte counts in the article Leukopenia.
When are there too many leukocytes in the blood?
An increased number of white blood cells is called leukocytosis. It can be caused, for example, by infections, inflammatory diseases or tumor diseases. In leukemia (blood cancer), for example, pathologically altered and immature leukocytes (blasts) can be released in very large numbers.
You can read everything important about elevated leukocyte levels and their possible causes in the article Leukocytosis.
What to do if the leukocyte value is changed?
If the leukocyte count is elevated due to an infection, it is possible to wait until the symptoms have subsided. If dangerous diseases such as blood cancer or autoimmune diseases are suspected, further organ examinations must follow. Sometimes no reason can be found for an elevated leukocyte count. This is then referred to as “idiopathic leukocytosis”.
