What are Monocytes?
Monocytes are a type of white blood cell (leukocytes) in your immune system.
Monocytes reside in your blood and tissues to find and destroy germs (viruses, bacteria, fungi and protozoa) and eliminate infected cells. Monocytes call on other white blood cells to help treat injury and prevent infection.
Monocytes turn into macrophage or dendritic cells when an invading germ or bacteria enters your body. The cells either kill the invader or alert other blood cells to help destroy it and prevent infection.
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.
What do Monocytes do?
Monocytes, along with other kinds of white blood cells, help the body fight disease and 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.
What is ‘Monocytes (absolute)’?
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.
Where are monocytes formed?
Monocytes form in bone marrow from undifferentiated blood cells, which are blood stem cells that have not 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.
What do monocytes look like?
Monocytes are the largest type of white blood cell and are nearly twice the size of a red blood cell. Under a microscope, monocytes are easy to identify based on their size. Monocyte cells have a two-bodied nucleus (bilobed nuclei) center that floats in a contained fluid called cytoplasm.
What is a normal range for my monocyte count?
Conditions vary based on the number of monocytes in your blood. Your monocyte count can be too high or too low as a result of your body fighting an infection or disease. A normal monocyte count is between 2% and 8% of your white blood cell count. This equals about 200 to 800 monocytes per microliter of blood in healthy adults. If your monocyte count is outside those ranges, you are at risk of acquiring a monocyte-related condition.
A note on reference ranges:
The percentage (%) reference ranges for Monocytes has not been officially established by most laboratories. If ranges have not been established by your laboratory, please refer to your Monocytes absolute count.
References:
Espinoza VE, Emmady PD. Histology, Monocytes. 2022 Apr 28. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 32491550.
The complete blood count: A guide for patients with cancer. (2018). uihc.org/health-topics/complete-blood-count-guide-patients-cancer
Espinoza V, et al. (2021). Histology, monocytes. ncbi.nlm.nih.gov/books/NBK557618/
Low white blood cell counts (neutropenia). (2000). cancer.org/treatment/treatments-and-side-effects/physical-side-effects/low-blood-counts/neutropenia.html
Macrophage. (n.d.). cancer.gov/publications/dictionaries/cancer-terms/def/macrophage
Monocyte. (n.d.). cancer.gov/publications/dictionaries/cancer-terms/def/monocyte
Understanding blood counts. (n.d.). lls.org/managing-your-cancer/lab-and-imaging-tests/understanding-blood-counts
What causes low monocyte levels?
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:
- 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
- Having low levels of monocytes may mean your body is more susceptible to infection.
Monocytopenia can predispose you to infections.
The bone marrow produces monocytes, and any condition that affects the bone marrow can affect the production of monocytes and other white blood cells.
Cancer treatments:
Common causes of low monocytes are treatments intended to lower immune function. Cancer treatments such as chemotherapy and radiation therapy can cause monocytopenia, as well as leukopenia and anemia. Cancers that invade the bone marrow, such as chronic myelomonocytic leukemia (CMML), or diseases that affect bone marrow function, can also cause a low monocyte count.
Immune system medical conditions:
Low monocytes can occur due to severe medical conditions that involve the immune system, such as anaphylaxis (a severe allergic reaction), sepsis (a whole-body reaction to a blood infection), and severe trauma.
Injury:
Sometimes a low monocyte level is associated with prolonged recovery from an injury.
GATA2 Deficiency:
This hereditary condition is inherited in an autosomal dominant pattern, meaning that anyone who inherits one gene from one parent for the disease will develop the condition. This condition commonly causes monocytopenia, and it can cause neutropenia (low neutrophils) or aplastic anemia (lack of blood cell production) as well. The effects can begin as early as infancy or as late as adulthood. Symptoms can include lymphadenopathy, warts, and frequent viral, fungal, and bacterial infections, including mycobacterial infection. This condition can also progress to cause acute myeloid leukemia or chronic myeloid leukemia.
Hairy Cell Leukemia:
Hairy cell leukemia is a type of blood cancer in which the body makes too many B-cell lymphocytes. It causes low levels of many types of leukocytes, including a low number of monocytes. The condition causes an enlarged spleen and a predisposition to infections. This type of cancer can be treated with medication or a bone marrow transplant (bone marrow is replaced with healthy stem cells from the recipient or a donor).
What are symptoms of low monocyte levels?
Low or high numbers of monocytes do not usually cause symptoms. However, people may have symptoms of the disorder that caused the change in monocyte number. Monocytopenia can cause symptoms, but symptoms may not result or be noticed, especially early on. When you have low monocytes, this reduces your body's immune defenses. The most common effect of monocytopenia is frequent infections, which can cause a range of symptoms.
Noticeable symptoms include:
- Lymphadenopathy (swollen lymph nodes)
- Fevers
- Nausea, vomiting, diarrhea
- Swelling, pain, or discomfort
Your symptoms can be caused by your low monocyte count or by other blood cell abnormalities, such as leukopenia (low white blood cells) or anemia (low numbers of healthy red blood cells).
How is a low monocyte count diagnosed?
Low monocyte levels or monocytopenia is diagnosed with a complete blood count (CBC). If your monocyte count is low, your doctor will likely run other tests to evaluate the cause. These can include a blood smear (blood is prepared on a slide, stained, and examined under a microscope in a lab), a genetic test, a bone marrow biopsy (a sample is taken from inside a bone and analyzed in the lab), or imaging tests.
What are possible treatment options of low monocyte levels or monocytopenia?
Treatment includes managing complications, treating the underlying condition, and preventing infections.
The causes of low monocytes are varied, and the cause often directs the treatment. If you chronically have a low monocyte count, your doctor may recommend infection prevention strategies. These may include staying up to date on recommended immunizations and avoiding places where you could be exposed to infections.
You may also need periodically scheduled CBCs or other tests so that complications, especially leukemia, can be identified and treated at an early stage.
If you develop a complication, such as an infection, this will need to be treated.
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A high levels of monocytes is called monocytosis.
If you have monocytosis, it means you have an abnormally high number of infection-fighting monocytes.
Monocytes are a specific type of white blood cell that protects your immune system from toxic or foreign substances. A high monocyte count does not necessarily mean you have a serious medical condition. If you have monocytosis, your healthcare provider will take a close look at your overall health so they can identify and treat any underlying cause.
What causes a high level of monocytes?
A high monocyte count is a potential sign of many different medical conditions. It is often linked to infectious diseases like mononucleosis or an autoimmune disease like lupus. Some medications can cause monocytosis. It’s also linked to conditions such as blood disorders and certain cancers. But you can develop a high monocyte count for reasons that are less serious. For example, chronic stress or challenging workouts can cause monocytosis. Pregnancy can also cause monocytosis.
What are possible symptoms of a high monocytes count?
Monocytosis does not usually cause symptoms. Instead, you may have symptoms of the medical condition that caused your high monocyte count.
A high monocyte count is a sign of several medical conditions that are treated in different ways. Once you and your provider know the underlying cause, you’ll have a better idea of how your condition may affect your daily life.
A high monocyte count is often associated with chronic or sub-acute infections. It can also be linked with some types of cancer, especially leukemia. A high monocyte count can occur when you are recovering from an acute infection.
Some conditions that can cause monocytosis include:
- Autoimmune and inflammatory diseases (including lupus, rheumatoid arthritis, ulcerative colitis, and inflammatory bowel disease)
- Syphilis, a sexually transmitted disease
- Collagen vascular disorders, an inflammation of the collagen and joints
- Sarcoidosis, an inflammatory disease
- Protozoan or rickettsial infections
- Bone marrow recovery
- Hematologic disorders, which affect your blood
- Some medications (including radiation therapy and cyokine therapy)
- Chronic infections (including tuberculosis, malaria, and endocarditis)
- Chronic stress
- Due to splenectomy (removal of the spleen)
- Heart attack
- Myeloproliferative disorders
- Viral infections (including COVID)
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