Monocytes are a type of white blood cell that comes from bone marrow. They can become either macrophage cells or dendritic cells.

Monocytes, along with other kinds of white blood cells, help the body fight disease and infection. When they become dendritic cells, they play a part in launching the inflammatory and anti-inflammatory processes that are part of your body’s immune response to infection. As macrophage cells, they can destroy microorganisms and foreign material, get rid of 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 certain medical treatments or bone marrow problems while high levels can indicate the presence of chronic infections or an autoimmune disease.

Monocytes are the largest of the white blood cells and are 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. These are both different kinds of white blood cells.

Dendritic cells use receptors to show the antigens to other immune system cells. They can 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, several types 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, such as the spleen, liver, and lungs, as well as bone marrow tissue, 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 to 8 percent 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 rangeAbsolute monocytes per microliter of blood (mcL)
Adults0.2 to 0.95 x 103
Infants from 6 months to 1 year0.6 x 103
Children from 4 to 10 years0.0 to 0.8 x 103

These numbers are from Allina Health and the ranges can vary slightly by health system. Your report may include a reference range provided by the lab that performs your test.

Men tend to have higher monocyte counts than women.

While having levels that are higher or lower 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 body’s immune system. Checking these levels is an important way to monitor your body’s 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.

Common conditions that could lead to a spike in abs monocytes can include:

Your absolute 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 levels of monocytes tend to develop as a result of medical conditions that lower your overall white blood cell count or disease treatments that suppress the immune system.

Causes of low absolute monocyte count can include:

Having low levels of monocytes may mean your body is more susceptible to infection.

If your white blood cell count is low, you may also have low absolute monocytes. Causes of a low white blood cell count can include:

  • infection
  • certain medications, including chemotherapy
  • malaria
  • alcoholism
  • lupus

Having an irregular monocyte count, whether low or high, is not a condition in and of itself. Rather, 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. If you have an annual physical that includes regular blood work, a CBC is fairly standard. 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 certain 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, or signs of inflammation.

Both a standard CBC and blood differential test are done by drawing a small amount of blood from a vein in your arm. The blood samples are sent to a lab and the various components of your blood are measured and reported back 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 of white blood cells 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 percent of them. Neutrophils fight against 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 percent of your white blood cells. But they can increase that percentage if you’re fighting off an allergy. They also increase their numbers 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 main cells in the lymph nodes.

Absolute monocytes are a measurement of a particular type of white blood cell. Monocytes are helpful at fighting 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 your blood. If you haven’t had a complete blood count done lately, ask a doctor if it’s time to get one.