Monocytes are a type of white blood cell. An increase or decrease in their number in the blood can be linked to different sick, benign or malignant. 

Monocytes are a type of white blood cell (or leukocyte). They represent 2 to 10% of the white blood cells circulating in our blood. 

These cells have a very short lifespan in the blood (about 24 hours). They then pass into the tissues where they differentiate into macrophages (the main phagocytic cells of the immune system). 

Defense of the body 

Monocytes like other white blood cells participate in the body’s specific defenses. 

They have the role of protecting and defending the body against bacteria, foreign substances, viruses, parasites, toxins and tumor cells.

The more precise role of monocytes is to present antigens to lymphocytes. They are also responsible for phagocytosis: they ingest and destroy pathogens and small cell residues. 

High level of monocytes (monocytosis)

An increase in the number of monocytes in the peripheral blood is associated with infections (brucellosis, salmonellosis, syphilis, tuberculosis, etc.), the recovery phase following neutropenia (decrease in the total number of white blood cells) and inflammatory conditions. chronic (rheumatoid arthritis, systemic lupus erythematosus, haemorrhagic rectoccolitis, Crohn’s disease, sarcoidosis, etc.) but also to pathologies of the hematological system (myeloproliferative neoplasias or acute leukemias, for example).

Low monocyte count (monocytopenia)

A decrease in monocyte counts may be due to a blood infection, chemotherapy, or a bone marrow disorder. Certain skin infections and human papillomavirus infection of the genitals can also cause low monocyte counts. This is also the case after administration of corticosteroids. 

Treatment of monocyte disorders, such as monocytopenia, depends on the cause. 

When the monocytosis is reactive (transient), in the event of bacterial infection for example, the treatment of the cause makes it possible to solve the problem in a few weeks or a few months. 

When the monocytosis is linked to myeloproliferative neoplasias or acute leukemias, the treatment depends on the disease (chemotherapy, bone marrow transplant). 

A blood test is used to analyze the white blood cell count (Blood Formula Count or CBC). This white blood cell count indicates their number in a 1 mm3 blood sample. It is normally less than 11 / mm000. When it is greater than this value, it may indicate an activation of the immune system in response to infection, inflammation, necrosis or even a malignant disease (Marieb, 3). 

A blood test also allows you to see the leukocyte formula which analyzes each type of white blood cell. It allows you to see the proportion of each type of white blood cell. The normal absolute value of monocytes is 100-700 / mm3. It is possible that the total white blood cell count is normal but the concentration of one type of white blood cell is higher or lower than normal.