What Is Monocytopenia?

Monocytes are a type of white blood cell that helps the body fight infections and other diseases. They are made in the bone marrow, and they work throughout the body. Some health conditions can cause monocytopenia, which is a low number of monocytes. Monocytopenia can predispose you to infections.

Monocytopenia usually is associated with abnormalities of other types of white blood cells. This can cause health problems, such as inflammation, severe infections, bleeding, or symptoms of anemia (including fatigue, dizziness, and pale skin). 

What Is Monocytopenia? 

Monocytopenia is a low monocyte count. Monocytes compose approximately 4%–8% of the total number of white blood cells.

Monocytes are produced in the bone marrow and circulate in the blood to the peripheral tissues, where they become dendritic cells and macrophages, which are:

• Dendritic cells detect infectious organisms (examples are viruses, bacteria, and fungi) and release chemicals to activate the immune response. 
• Macrophages destroy infectious organisms. 

How Are Monocytes Measured?

Monocyte count can be measured with a complete blood count (CBC). This test provides an absolute monocyte count and a monocyte count as a percentage of the total leukocyte (white blood cell) count. 

Widely accepted standard values are listed below, and some laboratories may have slightly different standard values. The absolute number is measured in cells per cubic millimeter.

Your CBC will also include a breakdown of the other types of white blood cells, as absolute numbers and percentages of total leukocytes.

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. 

Effects of Monocytopenia

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). 

What Are the Causes of Monocytopenia?

The bone marrow produces monocytes, and any condition that affects the bone marrow can affect the production of monocytes and other white blood cells.  

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. 

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. Sometimes a low monocyte level is ssociated 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).

Treatment 

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.

Summary

Low monocyte levels or monocytopenia can be caused by any problem that reduces the body’s white blood cell count. This includes chemotherapy, a bloodstream infection, or a bone marrow disorder. In some situations, monocytopenia can be a response to a severe medical problem, such as trauma, sepsis, or anaphylaxis.

The condition is diagnosed with a CBC, and other tests may be needed to identify the cause. Treatment includes managing complications, treating the underlying condition, and preventing infections.

A Word From Verywell 

If you have a low monocyte count, you and your healthcare provider should discuss it. Your provider will evaluate your low monocyte level along with other blood test results. Once you get a diagnosis, you can watch for early signs of complications as you proceed with your treatment. Early medical attention, if needed, can help you avoid serious complications.