What Do High Monocyte Levels Mean?

A high monocyte count can be a sign of illness

Monocytes are a type of white blood cell. They work as part of the immune system to help fight infections and disease. Monocytosis, which is a high monocyte count, can be temporary when it’s a normal response to an infection.

Monocytosis can also occur due to diseases such as cancer, in which case a high monocyte count may be persistent and require treatment. Having excessive monocytes due to disease can be associated with inadequate monocyte function, a predisposition to infection, and other blood cell abnormalities.

This article will discuss the role of monocytes and the normal range for them in the blood. It will explore what might cause a high monocyte count, what it means for your health, and what treatment or management might be needed.

Monocytes are a type of immune cell

SEBASTIAN KAULITZKI/SCIENCE PHOTO LIBRARY / Getty Images

What Are Monocytes?

Monocytes are a category of white blood cells formed in the bone marrow. They are larger than most blood cells. Monocytes compose approximately 4%–8% of white blood cells.

From the bloodstream, monocytes migrate into different tissues, where they differentiate and perform specialized functions. These include:

  • Dendritic cells monitor the tissues that line your body, identify infectious organisms (like bacteria, viruses, and fungi) and release chemicals to activate an immune response in the affected area. 
  • Macrophages contain chemicals that directly destroy pathogens (disease-causing infectious organisms). 

Blood Test for Absolute Monocytes

You can have your monocytes measured with a complete blood count (CBC) with differential. This is a blood test that measures your blood cells and provides a detailed breakdown of the number and proportion of different types.

This test can help determine whether specific blood cells are high or low and whether the proportion of certain types of blood cells is normal or abnormal. 

Normal Range for Monocytes

The number of white blood cells and the percentage of different types of white blood cells have an accepted normal range. Monocytes are measured as an absolute number per cubic millimeter (cu Mm) and as a percentage of white blood cells.

Normal Levels of Monocytes and White Blood Cells
   Per cu Mm  Percent of white blood cells
White blood cells  5,000–10,000 100
Monocytes  200–800 4–8

Your monocyte number can be a valuable tool for diagnosing disease. It is also important to look at this number and percentage considering other blood cell measurements.

Some medical issues that cause monocytosis may also cause anemia (low number of healthy red blood cells), thrombocytopenia (low platelets), or high or low numbers of other types of white blood cells.

The World Health Organization (WHO) defines persistent monocytosis as an absolute monocyte count of more than 1,000 per cu Mm, with monocytes accounting for more than 10% of white blood cells and persisting for longer than three months.

Causes and Risk Factors

Monocytosis develops due to the overproduction of monocytes in the bone marrow, which can be caused by various medical issues. It can occur as a temporary situation, when the body needs monocytes, such as in a bacterial or viral infection.

It can also occur due to a genetic mutation that alters the body’s production of white blood cells. Such a genetic mutation may affect only monocytes, or it could affect other white blood cells too. Usually, these genetic changes are acquired from environmental or other factors and not inherited in families.

Causes of increased monocytes include:

  • Bacterial infections such as tuberculosis
  • Viral infections such as COVID-19 
  • When bone marrow is recovering after immunosuppressive treatment 
  • As a medication-induced side effect 
  • Due to splenectomy (removal of the spleen) 
  • Leukemia, especially chronic myelomonocytic leukemia (CMML)
  • Polycythemia vera (a condition in which red blood cells and other blood cells are overproduced) 
  • Primary myelofibrosis (buildup of scar tissue in the bone marrow, where blood cells are produced)

High Monocytes and Health

If you have a high monocyte count that is not transient (lasting only a short while) but persists, there could be something wrong with your health. Your symptoms, physical examination, and your other diagnostic tests would help determine the cause of your monocytosis. For example, a fever and a cough may indicate an infection. 

Other diagnostic tests you might need include:

  • Chest X-ray 
  • Blood smear (a sample of blood that's stained and analyzed under a microscope in the lab)
  • Urine culture, blood culture, or throat culture (samples that are checked in the lab for disease-causing organisms)
  • Bone marrow biopsy (a sample of bone marrow that's removed and analyzed in the lab)

The impact of high monocytes on your health is tied to the cause of your monocytosis. In some cases, the increased monocytes are beneficial, such as during an infection or when your bone marrow is recovering after treatment. At other times, the high monocytes indicate a medical condition that requires treatment. 

Treatment for High Monocyte Count

Treatment for monocytosis depends on the cause. It may include antibiotic medication for a bacterial infection or chemotherapy or other cancer treatments for an illness like leukemia (cancers of the blood). Treatment for CMML can improve survival and quality of life.

Sometimes an associated condition may need to be treated as well. For example, anemia may need to be treated with therapies such as a blood transfusion or erythropoietin (a hormone that stimulates red blood cell production). 

Managing Monocyte Levels

During your treatment, you may need to have your monocyte levels checked repeatedly at regular intervals to monitor the effectiveness of your treatment. For some types of leukemia, all blood cells are periodically monitored to determine the effects of treatment.

Summary

Monocytes are a type of white blood cell that play a role in your immune system. Monocytosis (a high monocyte count) can occur along with changes in other leukocytes (white blood cells), or monocytosis may be the only indication of a medical problem.

Common causes of a high monocyte count include infections, leukemia, polycythemia vera (an increase in all blood cells, especially red blood cells), and primary myelofibrosis (buildup of scar tissue in the bone marrow, where blood cells are produced). If you have a high monocyte count, you may need diagnostic testing to determine the cause, and you may need treatment for the medical illness that is causing monocytosis. 

A Word From Verywell

It is normal to be concerned about an unusual result on your lab report, such as monocytosis, but this condition can have many causes. Talk to your healthcare provider to understand what may be causing it and get a diagnosis. If you need treatment, you will likely have your monocytes measured again to assess how well your treatment is working. 

Frequently Asked Questions

  • What are the signs and symptoms of high monocytes?

    Monocytes generally comprise a small percentage of white blood cells, and monocytosis might not cause obvious symptoms. You are more likely to experience symptoms of an illness that caused monocytosis than to experience symptoms of monocytosis.

    Sometimes, high monocytes can cause inflammation or fatigue. And monocytosis that develops due to cancer can occur along with other blood cell problems that could be symptomatic—such as anemia, thrombocytopenia, or leukopenia (low white blood cells).

  • Can stress increase monocyte levels?

    In general, while emotional or physical stress may be associated with slightly increased monocytes, it is not considered an explanation for high monocyte levels. Some research suggests that exercise can temporarily increase monocyte levels in some people.

    If your monocytes are high, your healthcare provider will likely look for medical causes first when considering a diagnosis.

  • Does depression cause high monocytes?

    Research suggests that white blood cell counts may be altered by depression, but this is not a consistent correlation. Checking monocyte counts also is not considered a reliable way to diagnose depression or to determine whether depression is adequately treated.

  • Is there a way to naturally lower your monocytes?

    No, there is not a natural treatment to lower monocytes. If you have a high monocyte count, it’s likely due to an infection or another medical cause.

    If your monocytes are elevated due to an infection, they will get back to normal levels when the infection resolves. If they are elevated due to a medical condition, you would need medical treatment.

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