Monocytopenia Symptoms and Causes

Monocytopenia describes a low number of monocytes, a type of white blood cell. Monocytes are made in the bone marrow and account for 2% to 6% of white blood cells at any given time. They work throughout the body as infection-fighting macrophages and dendritic cells. Your monocyte count, normally above 100 or below 500 cells per microliter, can be determined with a complete blood count (CBC).

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). It also can occur with cancer and other illnesses.

Symptoms

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.

Frequent infections are common, which can cause a range of symptoms. These 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). 

Causes

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

Low monocytes can occur due to:

• Anaphylaxis (a severe allergic reaction)
• Sepsis (a whole-body reaction to a blood infection)
• Severe trauma
• Human immunodeficiency virus (HIV) infection

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.

Common medical treatments can affect monocytes. These causes can include:

• Hemodialysis treatment for kidney failure
• Corticosteroid medication use
• Cancer treatments such as chemotherapy and radiation therapy

Sometimes a low monocyte level is associated with prolonged recovery from an injury. 

GATA2 Deficiency 

GATA2 deficiency symptoms 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.

It is inherited in an autosomal dominant pattern, meaning that anyone who inherits one gene from one parent for the disease will develop the condition. GATA2 deficiency commonly causes monocytopenia, and it can cause neutropenia (low neutrophils) or aplastic anemia (lack of blood cell production) as well. 

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).

Diagnostic Tests

If your CBC shows that your monocyte count is low, other tests may be needed to evaluate the cause. These tests can include:

• A blood smear (blood is prepared on a slide, stained, and examined under a microscope in a lab)
• Genetic testing (certain genetic conditions lead to monocytopenia)
• Imaging tests
• A bone marrow biopsy (a sample is taken from inside a bone and analyzed in the lab)

Depending on results, specialist care and testing may be needed.

Treatment 

If you have a low monocyte count on repeat tests, your healthcare provider 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. Keep in mind that causes of low monocytes are varied, and treatments are based on cause.

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 that may be needed to identify the cause. Treatment includes managing complications, treating the underlying condition, and preventing infections.