Causes of High Monocyte Count


Monocytes are a type of white blood cell that plays a crucial role in the immune system’s response to infection and inflammation. A high monocyte count, also known as monocytosis, can indicate various underlying health conditions. In this article, we will explore the different causes of elevated monocyte levels, ranging from infections to autoimmune disorders.


Infections are one of the most common causes of an increase in monocyte count. When the body encounters an infection, monocytes are recruited to the site of infection to help eliminate the pathogens. Some infections that can lead to monocytosis include:

  • Bacterial Infections: Certain bacterial infections, such as tuberculosis, endocarditis, and brucellosis, can trigger an elevated monocyte count.
  • Viral Infections: Viral illnesses like infectious mononucleosis, cytomegalovirus (CMV) infection, and viral hepatitis can also cause monocytosis.
  • Fungal Infections: Certain fungal infections, such as histoplasmosis and cryptococcosis, may result in increased monocyte levels.

It’s important to note that the specific type of infection and its severity can influence the degree of monocytosis observed.

Inflammatory Disorders

Various inflammatory conditions can lead to a high monocyte count. Inflammation is the body’s response to injury or harmful stimuli, and monocytes are involved in the inflammatory process. Some examples of inflammatory disorders that can cause monocytosis are:

  • Rheumatoid Arthritis: This chronic autoimmune disease characterized by joint inflammation can result in elevated monocyte levels.
  • Inflammatory Bowel Disease (IBD): Conditions like Crohn’s disease and ulcerative colitis, which cause chronic inflammation in the gastrointestinal tract, can lead to monocytosis.
  • Sarcoidosis: A multisystem disorder characterized by the formation of granulomas in various tissues, including the lungs and lymph nodes, can cause an increase in monocyte count.

Monocytosis | High Monocyte Count | Types, Causes, Symptoms, Treatment Of Monocytopenia |

Autoimmune Disorders

Autoimmune disorders occur when the immune system mistakenly attacks healthy cells and tissues. Some autoimmune conditions associated with monocytosis include:

  • Lupus: Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that can lead to elevated monocyte levels.
  • Sjögren’s Syndrome: This autoimmune disorder primarily affects the salivary glands and tear ducts, and it can be accompanied by monocytosis.
  • Vasculitis: Certain types of vasculitis, such as giant cell arteritis and Takayasu arteritis, can cause an increase in monocyte count.

Other Causes

Aside from infections, inflammatory disorders, and autoimmune conditions, there are other factors that can contribute to monocytosis. These include:

  • Chronic Myelomonocytic Leukemia (CMML): CMML is a type of cancer that affects the bone marrow and leads to increased monocyte production.
  • Medications: Certain medications, such as corticosteroids, can induce monocytosis as a side effect.
  • Smoking: Studies have shown that smoking can cause a rise in monocyte count, potentially due to the inflammatory effects of smoking on the body.


Elevated monocyte levels can be indicative of various underlying health conditions, ranging from infections to autoimmune disorders. It is crucial to identify the cause of monocytosis to determine the appropriate course of treatment. If you experience persistently high monocyte counts, it is recommended to consult a healthcare professional for further evaluation and guidance.

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