The white blood cell count is data that allows us to assess whether there is an infection. In the event of attack by a pathogenic microorganism, the level of white blood cells increases transiently. We are talking about hyperleukocytosis.
1. What is the normal white blood cell count?
White blood cells are immune cells responsible for defending the body against pathogenic microorganisms. White blood cells, also called leukocytes, bring together different cells: lymphocytes, polymorphonuclear cells or even monocytes and macrophages. The white blood cell count is often assessed to check for infection. Normal white blood cell count is usually between 4,000 and 11,000 cells per microliter, according to the MSD Manual. This level can thus sometimes be reduced, we speak of leukopenia, or sometimes be increased, we speak of hyperleukocytosis. Hyperleukocytosis can be transient or chronic. It can be moderate or severe.
2. What are the most common causes of high white blood cell counts?
Hyperleukocytosis exists when the number of white blood cells is greater than 10,000 leukocytes per mm3. In the vast majority of cases, an increase in white blood cell levels is indicative of an infection. Indeed, to fight against pathogens, the body will multiply the number of immune cells. Sometimes certain medications, such as corticosteroids, can cause an increase in white blood cells. An increase in certain white blood cells can be specific to a pathology. Thus, an increase in monocytes can be linked to inflammation or an infection, an increase in neutrophils is characteristic of a bacterial infection, an increase in eosinophils is characteristic of an allergic or parasitic reaction; finally, an increase in polynuclear basophils is characteristic of an allergic or infectious reaction. Other situations can explain a transient increase in the level of white blood cells, such as intense physical exertion, pregnancy or even a very strong emotion.
3. What are the rarer causes of too high a white blood cell count?
Sometimes, an increase in the number of white blood cells can reveal a pathology unrelated to an infectious problem. Certain cancers, such as leukemia for example, can cause an increase in the level of these cells. This should be mentioned in particular when the increase in the number of white blood cells is not transient. It should be noted that in cases of malignant hemopathy, the level of white blood cells is very high, we then speak of severe leukocytosis. Stress or other rare pathologies, such as leukocyte adhesion deficiency, which affects less than 350 people per year, according to the Leukocyte adhesion deficiency sheet on the Orphanet site, can also be responsible for hyperleukocytosis.
Sources
- Overview of White Blood Cell Diseases, Dr. David C. Dale, The MSD Manual – Consumer Version, April 2023
- Leukocyte adhesion deficiency, Orphanet, the knowledge portal on rare diseases and orphan drugs