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Monocytes: Normal, High & Low Levels

Written by Maja Stanojevic, MD | Reviewed by Nattha Wannissorn, PhD (Molecular Genetics) | Last updated:
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology), Puya Yazdi, MD | Written by Maja Stanojevic, MD | Reviewed by Nattha Wannissorn, PhD (Molecular Genetics) | Last updated:

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Monocytes are the largest of all white blood cells and play an important role in the defense against germs and in inflammation. Read on to learn about the normal range of these cells and the health implications of abnormal levels.

What are Monocytes?

The Front Lines of Your Immunity

Monocytes are the largest type of white blood cell. Approximately 2 to 10% of white blood cells are monocytes [1].

These immune cells circulate in the blood for several days before they enter the tissues, where they become macrophages or dendritic cells [1, 2].

Monocytes protect against viral, bacterial, fungal, and protozoal infections. They kill microorganisms, ingest foreign particles, remove dead cells, and boost the immune response [3, 1, 4, 2].

However, they can also be involved in the development of inflammatory diseases like arthritis and atherosclerosis. In this post, we’ll take a closer look at how monocytes work and how they may be implicated in disease [5, 6, 7].

Monocytes can kill microbes, boost your immunity, and remove dead cells. Once they enter your tissues, they become macrophages.

Production

All blood cells originate from common parent cells called hematopoietic stem cells. In adults, blood cells are produced mainly in the bone marrow; this process is called hematopoiesis. The process of monocyte production in particular is called myelopoiesis [8, 9].

Myelopoiesis is subject to a complex regulatory system, including such factors as:

  • Transcription factor SPI1 [10, 11, 12, 13].
  • Cytokines: SCF (stem cell factor), GM-CSF (granulocyte-macrophage-colony-stimulating factor), M-CSF (macrophage colony-stimulating factor, CSF1), IL-3, IL-6, and IFN-gamma [14, 15, 16, 17].

Stem cells in your bone marrow produce monocytes and other blood cells. Different transcription factors and cytokines control this process.

After Monocytes Fulfill Their Job, What Happens Next?

Monocytes live for an average of three days before undergoing apoptosis (programmed cell death). They live longer during periods of high inflammation; once inflammation resolves, cell death occurs [18, 19].

Monocyte Reference Ranges

The normal ranges for monocytes may be reported in a few different units. Ask your doctor to help you interpret your lab test results. The normal ranges are:

  • 0.2 – 0.8 x10^9/L
  • 200 – 800 / microL
  • 1 – 10%

Monocyte counts within these ranges are associated with reduced rates of:

  • Viral, bacterial, and fungal infections [20]
  • Heart Disease [21]
  • Obesity [22]
  • Diabetes [22]
  • Death (mortality) [23]

Again, it’s important to talk to your doctor if you think something may be wrong. Other suggested marker tests you may want to ask about if your monocytes are out of the optimal range include:

Optimal monocyte count is associated with reduced rates of infection and chronic disease. If your monocytes are high or low, you may want to ask your doctor to check your levels of other white blood cells.

High Levels of Monocytes (Monocytosis)

Monocytosis is a condition in which the number of monocytes circulating in the blood is increased to more than 0.8×109/L in adults.

Conditions Associated with Monocytosis

  • Blood disorders (myelodysplastic disorder, acute monocytic, chronic myelomonocytic leukemia, Hodgkin and non-Hodgkin lymphoma) [24, 25, 26]
  • Infections (tuberculosis, viral infections, bacterial endocarditis, brucellosis, malaria, syphilis) [27, 28, 29, 30, 31, 32]
  • Autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease) [33, 34, 35]
  • Sarcoidosis [36]
  • Cancers (ovary, breast, rectum) [27, 37]
  • Heart attack [27, 38]
  • Appendicitis [39]
  • HIV infection [27, 40]
  • Depression [41]
  • Childbirth [42, 43]
  • Obesity [44]
  • Severe pneumonia [45]
  • Alcoholic liver disease [46]

Causes shown here are commonly associated with this symptom. Work with your doctor or other health care professional for an accurate diagnosis.

Symptoms and Causes

Monocytosis most commonly occurs during and after chronic inflammation or infection [23].

However,several other conditions can also be associated with monocytosis, such as heart disease, depression, diabetes, and obesity [21, 22, 47].

The conditions most commonly associated with high monocyte levels are:

  • Chronic (long-term) inflammation [23]
  • Infections, such as tuberculosis, malaria, and syphilis [48, 49, 50]

High monocyte levels may also be linked to:

  • Autoimmune diseases, such as lupus, rheumatoid arthritis, and IBD [35, 33, 34]
  • Leukemias, such as chronic myelomonocytic leukemia, and juvenile myelomonocytic leukemia [51, 52]
  • Cancer [53]
  • Depression [41]
  • Obesity [54]

Few symptoms are considered to be caused by monocytosis itself. Instead, according to many researchers, symptoms arise from the diseases associated with monocytosis [22]. These symptoms include:

  • Fever [55]
  • Pain [56]
  • Swelling [55]

The main causes of high monocytes (monocytosis) are chronic inflammation and infections. Symptoms depend on the cause and may include fever, pain, and swelling.

Low Levels of Monocytes (Monocytopenia)

In monocytopenia, the number of monocytes circulating in the blood is decreased to less than 0.2×109/L in adults. Monocytopenia itself does not appear to produce symptoms, and patients usually only show symptoms related to an associated condition. Such symptoms may include fatigue and fever [20, 57].

Conditions Associated with Monocytopenia

  • Aplastic anemia [58]
  • Leukemia (hairy-cell leukemia, chronic lymphocytic leukemia) [59]
  • Chemotherapy [60]
  • MonoMAC syndrome (monocytopenia and Mycobacterium Avium Complex syndrome) [61]
  • Severe burn injuries [62]
  • Rheumatoid arthritis [63]
  • Systemic lupus erythematosus [64]
  • HIV infection [65]
  • Vitamin B12 deficiency [66]
  • Corticosteroid therapy (transient monocytopenia) [67]
  • Administration of INF-alpha and TNF-alpha [68]
  • Radiation therapy [69]

Autoimmune diseases, HIV, burns, and many other conditions and therapies are associated with reduced monocyte count; symptoms depend on the underlying cause.

Irregular Monocyte Levels?

Have you recently had your monocyte count tested? Want to learn about what your results mean? Check out these posts:

LabTestAnalyzer, a sister company of SelfHacked, helps you make sense of your lab results. It informs you which labs are not in the optimal range and gives you guidance about how to get them to optimal. It also allows you to track your labs over time. No need to do thousands of hours of research on what to make of your lab tests.

Takeaway

Monocytes are the largest of the white blood cells. They kill microbes, recycle old cells, and boost immunity. People with monocyte levels within the normal range (0.2 – 0.8 x10^9/L) tend to develop fewer infections and chronic diseases.

The most common causes of high monocytes (monocytosis) are chronic infections and inflammation. In turn, high monocytes can worsen inflammation and clog your blood vessels.

Many health conditions can also cause low monocyte levels (monocytopenia), including autoimmune diseases and nutrient deficiencies. Having low monocytes may reduce your risk of heart disease but makes you more prone to infections and blood disorders.

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