Monocytes are a type of white blood cell that come from bone marrow. Along with other kinds of white blood cells, they are part of the immune system and help your body fight disease and infection.
Monocyte count is often described as “monocytes (absolute),” which is the total number of monocytes in your blood.
You might also see it as a percentage of your total white blood cell count.
- Low levels of monocytes can result from specific medical treatments or bone marrow problems.
- High levels can indicate chronic infections or an autoimmune disease.
Monocytes are the largest white blood cells, about twice the size of red blood cells. They form in the bone marrow. Then, they enter the bloodstream and travel throughout the body before entering the tissue of the different organs to look for pathogens.
Once activated, they become macrophages or dendritic cells.
Dendritic cells use receptors to show antigens (foreign cells or parts of cells) to other immune cells. They cause monocytes to travel through the body to affected tissues.
Macrophages work with other white blood cells to kill microorganisms, fight cancer cells, and remove dead cells. One way they do this is by signaling to other cell types that an unwanted substance or cell is present. They also release toxic chemicals to kill harmful bacteria or infected cells. Macrophages can also digest germs that other WBCs have coated in antibodies.
Monocytes make up around 2% to 8% of your total white blood cell count.
Absolute monocyte count can vary slightly depending on the test method and other factors. Normal results for absolute monocytes for an adult are 0.2 to 08 x 109/L.
The range can vary slightly depending on how it’s measured. Your report may include a reference range from the lab that performs your test.
Males tend to have higher monocyte counts than females.
While levels outside the normal range aren’t necessarily dangerous, they may indicate an underlying condition that needs evaluation.
Monocyte levels can change depending on the activity of your immune system. Checking these levels helps monitor your immunity.
Your body may produce more monocytes when you have an infection or an autoimmune disease.
If you have an autoimmune disease, monocytes can mistakenly attack healthy cells in your body.
Conditions that can lead to a spike in monocytes include:
- chronic inflammatory diseases, such as inflammatory bowel disease
- bacterial infections, such as tuberculosis, brucellosis, syphilis, and subacute bacterial endocarditis
- leukemia and other types of cancer, including lymphoma and multiple myeloma
- sarcoidosis, a disease in which abnormal levels of inflammatory cells gather in multiple organs of the body
- Langerhans cell histiocytosis, a rare disorder that can damage tissue in the body
Your monocyte count may also be high if your white blood cell count is high. Causes of a high white blood cell count can include:
- infection or inflammation
- burns or injury
- autoimmune diseases, such as lupus and rheumatoid arthritis
- thyroid irregularities or malnutrition
- certain medications
Low monocyte count typically results from medical conditions that lower your white blood cell count or disease treatments that suppress the immune system.
Causes of low monocytes can include:
- chemotherapy and radiation therapy, which can injure bone marrow
- HIV, which weakens the body’s immune system
- sepsis, an infection of the bloodstream
Low monocyte levels may mean your body is more susceptible to infection.
You may also have low absolute monocytes if your white blood cell count is low. Causes of a low white blood cell count can include:
- infection
- certain medications, including chemotherapy
- malaria
- alcohol use disorder
- lupus
A low or high monocyte count is not a condition in itself. Instead, it is a sign of an underlying cause, whether due to illness, disease, infection, or certain medications.
Treatment typically involves treating the underlying condition. A doctor may recommend a blood differential test to get additional information to help diagnose your condition.
A standard complete blood count (CBC) will include a monocyte count. A CBC is fairly common if you have an annual physical that includes regular blood work.
CBC also checks:
- level of red blood cells, which carry oxygen to your organs and other tissues
- platelet count, which helps clot the blood and prevent bleeding complications
- hemoglobin level, the protein that carries oxygen in your red blood cells
- hematocrit, a ratio of red blood cells to plasma in your blood
Absolute monocyte count measures how many monocytes you have. Monocytes are a type of white blood cell that helps fight infections and diseases like cancer.
Getting your absolute monocyte levels checked as part of a routine blood test is one way to monitor the health of your immune system and blood.