Atypical amounts of these white blood cells are mainly caused by infection or a condition that affects your immune system. Treating the underlying condition can help raise or lower your monocyte levels.
Monocytes are a type of white blood cell that comes from bone marrow. Monocytes, along with other kinds of white blood cells, help the body fight disease and infection.
They can become either macrophage cells or dendritic cells, two types of white blood cells. When they become dendritic cells, they launch the inflammatory and anti-inflammatory processes that are part of your body’s immune response to infection. Macrophage cells can destroy microorganisms and foreign material, eliminate dead cells, and boost the body’s immune response.
A blood cell count measures the number of white blood cells in your blood. When you get a comprehensive blood test that includes a complete blood count, you may notice a measurement for monocytes. It’s often listed as “monocytes (absolute)” because it’s presented as an absolute number.
You may also see monocytes noted as a percentage of your white blood cell count rather than as an absolute number.
Low levels can result from specific medical treatments or bone marrow problems, while high levels can indicate the presence of chronic infections or an autoimmune disease.
Monocytes are the largest white blood cells, about twice the size of red blood cells. These powerful defenders aren’t plentiful in the bloodstream, but they’re vital in protecting the body against infection.
Monocytes move throughout the bloodstream to the tissues in the body. They rest until needed and then transform into macrophages or dendritic cells.
Dendritic cells use receptors to show the antigens to other immune system cells. They cause monocytes to travel through the body to the affected tissues.
Macrophages kill microorganisms and fight cancer cells. They also work with other white blood cells to remove dead cells and support the body’s immune system against foreign substances and infections.
One way macrophages do this is by signaling to other cell types that there is an infection. Together, various kinds of white blood cells then work to fight off the infection.
Monocytes form in bone marrow from undifferentiated blood cells, which are blood stem cells that haven’t yet changed to become a specialized cell type. After forming, monocytes then enter the bloodstream. They travel throughout the body before entering the tissue of the different organs to look for pathogens.
Monocytes rest until they’re activated.
Exposure to pathogens (disease-causing substances) can start the process of a monocyte becoming a macrophage. Once fully activated, a macrophage can release toxic chemicals that kill harmful bacteria or infected cells. Macrophages can digest germs if they have been coated by antibodies by other white blood cells.
Typically, monocytes make up 2-8% of your total white blood cell count.
Absolute monocyte test results can range slightly, depending on the method used for the test and other factors. According to Allina Health, a nonprofit healthcare system, normal results for absolute monocytes typically fall into these ranges:
| Age range | Absolute monocytes per microliter of blood (mcL) |
|---|---|
| Adults | 0.2 to 0.95 x 103 |
| Infants from 6 months to 1 year | 0.6 x 103 |
| Children from 4 to 10 years | 0.0 to 0.8 x 103 |
These ranges can vary slightly by health system. Your report may include a reference range from the lab that performs your test.
Males tend to have higher monocyte counts than females.
While having higher or lower levels than that range isn’t necessarily dangerous, it may indicate an underlying condition that needs to be evaluated.
Monocyte levels fall or rise depending on what’s going on with the immune system. Checking these levels helps monitor your immunity.
Your body may make more monocytes once an infection is detected or if you have an autoimmune disease. If you have an autoimmune disease, cells such as monocytes go after healthy cells in your body by mistake. People with chronic infections tend to have elevated levels of monocytes, too.
Conditions that can lead to a spike in abs 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 absolute monocyte count may also be high if your white blood cell count is high. Causes of an elevated 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 levels of monocytes typically develop due to medical conditions that lower your white blood cell count or disease treatments that suppress the immune system.
Causes of low absolute monocyte count can include:
- chemotherapy and radiation therapy, which can injure bone marrow
- HIV and AIDS, which weaken 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
- alcoholism
- lupus
An irregular monocyte count, whether low or high, is not a condition in and of itself. Instead, it is a sign of an underlying cause, whether illness, disease, infection, or taking certain medications.
Treatment typically involves treating the underlying condition. A doctor may first 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. In addition to checking your white blood cell count (including monocytes), a CBC checks for:
- red blood cells, which carry oxygen to your organs and other tissue
- platelets, which help clot the blood and prevent bleeding complications
- hemoglobin, the protein that carries oxygen in your red blood cells
- hematocrit, a ratio of red blood cells to plasma in your blood
A doctor may also order a blood differential test if they believe you may have abnormal blood cell levels. If your CBC shows specific markers are lower or higher than the normal range, this test can help confirm the results or show that the levels reported in the initial CBC were only temporarily out of the normal range.
A blood differential test may also be ordered if you have:
- an infection
- autoimmune disease
- bone marrow disorder
- signs of inflammation
A standard CBC and blood differential test involve drawing a small amount of blood from a vein in your arm. A lab measures the various components of your blood and reports the results to you and your doctor.
In addition to monocytes, your blood contains other types of white blood cells, all of which help fight off infections and protect you from disease. The types fall into two main groups: granulocytes and mononuclear cells.
Neutrophils
These granulocytes make up the majority of white blood cells in the body — up to 70% of them. Neutrophils fight infection and are the first white blood cells to respond to inflammation anywhere in the body.
Eosinophils
These are also granulocytes and represent less than 3% of your white blood cells. But that percentage can increase if you’re fighting off an allergy or when a parasite is detected.
Basophils
These are the fewest in number among the granulocytes but are especially helpful in fighting allergies and asthma.
Lymphocytes
Along with monocytes, lymphocytes are in the mononuclear cell group, meaning their nucleus is in one piece. Lymphocytes are the primary cells in the lymph nodes.
The following includes commonly asked questions about absolute monocytes.
What does it mean when your monocytes are low?
A low absolute monocyte count typically results from medications that injure the bone marrow, like some cancer treatments, or a condition that weakens your immune system, such as AIDS.
What level of monocytes indicates leukemia?
Having a high level of monocytes can be associated with leukemia. But a high level can also occur with a bacterial infection or chronic inflammatory disease, like IBS.
Can high monocytes mean heart disease?
An increased level of monocytes
What is a normal monocyte percentage?
Monocytes typically make up 2-8% of your total white blood cell count. Percentages outside of that range may have various causes from infection to a weakened immune system.
Absolute monocytes are a measurement of a particular type of white blood cell. Monocytes help fight infections and diseases, such as 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. If you haven’t had a complete blood count done lately, ask a doctor if it’s time to get one.