Monocytes are one of the five types of white blood cells that circulate through the body and play an integral part in the innate immune system, which is present at birth and acts as a first line of defense. Monocytes are essential for recognizing and eliminating pathogens, such as bacteria, fungi, and viruses (any organism that can cause a disease), and triggering inflammatory responses important for healing.
Varying levels of circulating monocytes can be a defining characteristic of the immune system's state, acting as a biomarker for diseases and infection. This article discusses the function of monocytes, insights on what varying levels may indicate, lab testing methods, and strategies for treating or managing elevated monocyte levels.
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What Are Monocytes?
Monocytes are essential components of the immune system. They detect and defend against pathogens and play a key role in inflammation.
Monocytes are made in the bone marrow, a soft tissue that fills bone cavities. They circulate in the blood for 1-3 days before migrating to other tissues, where they differentiate into macrophages and dendritic cells, the key resident immune cells.(38) Monocytes are highly effective in initiating immune responses and serve as a bridge between the innate and adaptive immune systems.
A normal monocyte count is between 2-8% of your white blood cell (WBC) count, or 200-800 monocytes/microliter (μL), and an elevated monocyte count is considered above 10% of your WBC count (or 1000 monocytes/µL).
Causes of High Monocytes
A high monocyte count, or monocytosis, generally indicates the immune system is activated. This may be caused by various factors, most commonly due to long-term infections, blood disorders, or autoimmune diseases.
Infections
An increased monocyte count may indicate an ongoing infection in the body. This can include bacterial (e.g., brucellosis, tuberculosis, syphilis, endocarditis), viral infections (e.g., COVID-19, infectious mononucleosis, mumps, and measles), or parasitic infections (e.g., malaria).
Inflammatory Conditions
Monocytes play a role in inflammation, which can cause their levels to rise in diseases characterized by chronic inflammation, such as inflammatory bowel disease (IBD), systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA).
Cancers
Monocytes have complex roles in cancer, both defending against and promoting tumor growth. Monocytosis is often observed in blood cancers such as leukemia and lymphoma, but elevated monocyte levels are generally considered to be a poor prognostic marker.
In leukemia, the bone marrow produces excessive immature and abnormal monocytes, while in lymphoma, monocytes can contribute to tumor growth in the tumor microenvironment, the ecosystem of cells inside and surrounding the tumor. Some forms of lymphoma can cause elevated monocyte counts as part of the body’s immune response to cancer.
Other Factors
Environmental and lifestyle factors, such as pregnancy, smoking cigarettes, and certain medications such as etoricoxib, propafenone, and tramadol can also lead to elevated monocyte levels due to systemic inflammation.(3)
Symptoms and Indicators
Monocytosis itself may not have any symptoms. Symptoms are typically related to the underlying condition causing the elevated monocyte count. Common symptoms include fatigue, weakness, and fever.
If your monocyte count is elevated, it’s important to consult a healthcare professional to identify and treat the underlying cause.
Lab Tests and Diagnosis
A complete blood count (CBC) is a standard blood test used to evaluate your overall health and detect various disorders, including anemia, infection, and other diseases. A CBC measures red and white blood cells, platelets, hemoglobin, and hematocrit. When combined with a differential blood test (known as CBC with differential), it can distinguish between different types of white blood cells, such as neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
This differentiation gives healthcare professionals a more detailed understanding of your overall health and the immune system response to potential threats. Additionally, these tests are crucial for monitoring ongoing treatments and ensuring they effectively manage any underlying conditions, particularly in patients with chronic diseases or those undergoing immunosuppressive therapies. Monocyte levels can be expressed as either:
- A percentage of white blood cells
- An absolute monocyte count (cells/μL) (3)
An absolute monocyte count is often more clinically useful because it directly measures monocytes in the blood, which can identify problems that may not be apparent when expressed as a percentage.
For example, a patient may have a normal percentage of monocytes compared to other white blood cells but a high total WBC count, indicating an elevated absolute monocyte count. Both measurements are valuable but serve different purposes in understanding the patient’s health.
Additional Testing and Biomarkers
It’s important to evaluate other biomarkers through additional testing to identify the root cause of monocytosis. A CBC with differential will show varying levels of other types of cells in the blood, providing a clearer picture of the underlying problem. Other inflammatory biomarkers can also be tested to narrow down infections and diseases.
Low Lymphocytes and High Monocytes
Lymphocytes are part of the adaptive immune system, which develops after birth to recognize and respond to pathogens by producing antibodies. This group includes B and T-cells in the blood and the lymph nodes.
Low lymphocytes and high monocytes can indicate the immune system’s response to tumor growth. Cancer can weaken or manipulate the immune system, particularly the adaptive immune system, allowing tumors to grow under the radar from immune surveillance without detection.
Normal lymphocyte levels range between 20-40% of total WBC count or 1000-4000 cells/μL.(16)
Low Neutrophils and High Monocytes
Neutrophils, like monocytes, are part of the innate immune system and act as a first line of defense against pathogens. They often recruit and assist in monocytic function.
Low neutrophils (neutropenia) and high monocytes may indicate an infection or autoimmune disease.
Normal neutrophil levels range between 40-60% of total white blood cell count or 1500-8000 cells/μL.(16)
Other Biomarkers
- Elevated ESR (erythrocyte sedimentation rate), commonly called sed-rate, and CRP (C-reactive protein) can indicate immune system activation, often linked to autoimmune diseases.
- Different CRP levels are correlated to different causes, but normal ranges are generally <0.3 mg/dL.
- Minor elevation (0.3-1.0 mg/dL) is observed in obesity, pregnancy, depression, diabetes, and cigarette smoking along with many others.
- Moderate elevation (1.0-10.0 mg/dL) is observed in autoimmune diseases (such as RA or lupus), bronchitis, pancreatitis, myocardial infarction, or malignancy.
- Marked elevation (>10.0 mg/dL) can indicate bacterial or viral infections, systemic vasculitis, or major trauma.
- Severe elevation (>50.0 mg/dL) is observed in acute bacterial infections.
Treatment Options for High Monocytes
Treating monocytosis involves addressing the underlying disease, which can vary depending on the condition. Identifying the root cause of monocytosis is critical for determining an appropriate treatment plan.
Infections:
Treatment focuses on managing symptoms of viral infections, whereas bacterial infections like tuberculosis (TB) may require antibiotics to lower monocyte levels. Different parasitic diseases may require additional lab tests to find the appropriate treatment.
Inflammatory Conditions:
Treatment consists of using anti-inflammatory or immunosuppressive medications, including steroids, to treat conditions like IBD, SLE, and RA.
Cancers:
Treating leukemia and lymphoma cancers includes chemotherapy, radiation therapy, stem cell transplant, and supportive therapy.
How to Manage High Monocytes
Maintaining monocyte levels within a healthy range is important, as low levels can weaken the immune system and increase susceptibility to illness.
Practicing a healthy lifestyle and exercising regularly is a great way to maintain monocyte levels and function, which is especially important as we age.(3)
Since monocytosis often results from immune activation and increased inflammation, eating anti-inflammatory foods can support immune function. The Mediterranean diet is an excellent choice, featuring foods like:
- Olive oil
- Leafy vegetables
- Nuts
- Fatty fish (salmon, tuna, sardines, and mackerel)
- Strawberries, blueberries, cherries and oranges
Avoiding inflammatory foods is equally as important. Some examples include:
- Red meat
- Refined carbohydrates
- Fried foods
- Limiting alcohol consumption
Above all, regular check-ups and open communication with your healthcare provider are essential for efficiently managing monocytosis by addressing the underlying cause and promoting a healthy lifestyle.
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Key Takeaways
- In conclusion, monocytes play a critical role in the immune system as part of the body’s first line of defense. Normal monocyte levels are essential for immune function, and elevated levels (or monocytosis) can signal underlying health issues such as:
- Infections
- Autoimmune diseases
- Cancer
- Diagnosing the cause of monocytosis typically involves lab tests like a Complete Blood Count (CBC) with differential, which provides insight into the different types of WBCs and overall immune activity.
- While some lifestyle modifications can help to manage monocyte levels, treating monocytosis requires addressing the root cause, depending on the underlying condition.
- Maintaining a healthy lifestyle can also be helpful in keeping monocyte levels within a healthy range and supporting overall immune function, including:
- Eating a balanced, anti-inflammatory diet
- Exercising
- Regular check-ups with your healthcare provider
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