When you get a comprehensive blood test that includes a complete blood count, you may notice a measurement for monocytes, a type of white blood cell. 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 an absolute number.

Monocytes and other kinds of white blood cells are necessary to help the body fight disease and infection. 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 three to four times the size of red blood cells. These big, powerful defenders aren’t plentiful in the bloodstream, but they’re vital in protecting the body against infections.

Monocytes move throughout the bloodstream to tissues in the body, where they transform into macrophages, a different kind of white blood cell.

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 myelomonocytic stem cells before entering the bloodstream. They travel throughout the body for a few hours before entering the tissue of organs, such as the spleen, liver, and lungs, as well as bone marrow tissue.

Monocytes rest until they’re activated to become macrophages. 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.

Typically, monocytes make up 2 to 8 percent of 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 non-profit healthcare system, normal results for absolute monocytes 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

Men tend to have higher monocyte counts than women.

While having levels that are higher or lower than that range aren’t necessarily dangerous, they 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.

The body may make more monocytes once an infection is detected or if the body has 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 include:

Interestingly, low levels of monocytes can be the result of autoimmune diseases, too.

Low levels of monocytes tend to develop as a result of medical conditions that lower your overall white blood cell count or treatments for cancer and other serious diseases that suppress the immune system.

Causes of low absolute monocyte count include:

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, a blood differential test can help confirm the results or show that the levels reported in the initial CBC were out of the normal range for temporary reasons.

A blood differential test may also be ordered if you have an infection, autoimmune disease, a 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 — as much as 70 percent. Neutrophils fight against all kinds of 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 your doctor if it’s time to get one.