What is monocytosis?

Monocytosis refers to an abnormally high monocyte count in the bloodstream. In healthy adults, the normal monocyte count ranges from 0.2 to 1.0 x 10⁹/L, or 2-8% of the total white blood cell (WBC) count.¹

What is a monocyte?

Monocytes are a type of white blood cell produced in the bone marrow. They circulate in the bloodstream and target specific areas of the body, where they differentiate into dendritic cells or macrophages. Macrophages eliminate dead cells, absorb foreign objects, encircle and destroy bacteria, and strengthen immune responses. Dendritic cells enhance immune responses during inflammation by presenting antigens on their surface to other immune system cells.²

Functions of monocyte

Monocytes have two primary functions: monitoring the body for microbial cells and organising an immune response in the event of infection or inflammation. They possess toll-like receptors on their surfaces that help detect invading microbes. Upon recognition of invasive cells, monocytes move from the bone marrow into the bloodstream within 12 to 24 hours and infiltrate tissues to eliminate the invader.²

What causes monocytosis?

Monocytosis is a sign of a wide range of medical conditions. It is often associated with chronic or subacute infections such as visceral leishmaniasis, syphilis, malaria, tuberculosis (TB), brucellosis, and rickettsial infections. Other causes include chronic inflammatory diseases (e.g., rheumatoid arthritis, inflammatory bowel disease), haematological disorders (e.g., chronic myelomonocytic leukaemia), and the recovery phase of acute infections.³

Symptoms of monocytosis

Monocytosis doesn't have any direct symptoms, instead, you will have symptoms of infection or a condition which caused Monocytosis. 

Diagnosis

Complete blood count (CBC)

The complete blood count (CBC) test is the first step in determining the cause of your monocytosis. Your clinician draws a blood sample to count the amount of blood cells. Because monocytes are a form of white blood cell, your provider may also look at how many other types of white blood cells are in your sample.

Peripheral blood smear

This test assists your provider in narrowing down the list of potential concerns. The size and structure of your cells are evaluated by your healthcare practitioner by looking at a sample of your blood under a microscope.

Absolute monocyte count

The amount of monocytes in your blood sample is determined by this test. Multiplying the percentage of monocytes in your CBC by the total amount of white blood cells yields an absolute monocyte count. Your doctor utilises this test result to determine if the number of monocytes in your body is normal, elevated, or decreased.⁴

Tuberculosis

What is tuberculosis (TB)?

It is an infection caused by the organism Mycobacterium tuberculosis.  It primarily affects the Lungs but rarely it also affects other parts of the body like the Brain, Kidney, and Spine.⁵

How does tuberculosis spread?

It spreads from person to person. When an active TB patient coughs, speaks or sneezes, the infectious bacteria in the throat or lungs get into the air. Depending on the type of space (indoor, outdoor, ventilation) the organism can stay up to several hours. When a healthy person inhales these germs they become infected.⁶

What are the symptoms of tuberculosis? 

TB has two forms: active (symptomatic) and inactive (asymptomatic). Inactive TB can become active if not treated.

Signs and symptoms of active TB include:

• Persistent cough (more than 3 weeks)
• Sputum with blood
• Coughing up blood
• Chest pain
• Weakness or tiredness 
• Sudden weight loss
• Loss of appetite
• Chills
• Fever
• Night sweat⁶

Diagnosis

Skin test

A small amount of tuberculin is injected under the skin on the forearm. A medical professional examines the site for swelling within 48 to 72 hours. A positive test indicates either active TB or a latent infection.

Blood test

The tests assess the immune response when a little amount of TB protein is mixed with the blood.

X-ray

If Irregular lung patches are seen on a chest X-ray, it may be indicative of active tuberculosis.

Sputum test

A sputum sample is analysed to detect TB bacteria. The lab will perform tests including a smear and a culture test. The laboratory will also do an antibiotic sensitivity test, to determine which antibiotics can kill TB bacteria effectively.⁷

Monocytosis and tuberculosis (TB)

Mycobacterium infection (TB) can produce different haematological alterations (changes in blood components), one of which is a change in monocyte count. Scientists have confirmed that, in TB patients there is a significant increase in monocytes.

Monocytes play two essential roles in TB infection. Firstly, they are vital in initiating the body's defences against TB-causing bacteria and triggering natural immune responses. Secondly, during tuberculosis, monocytes participate in the inflammatory response, which can lead to tissue destruction as 'collateral damage' while combating the bacteria. In response to this, the bacteria have adapted through natural selection to utilise monocytes as a means of transportation, allowing them to spread to different parts of the body.

The characteristic of tuberculosis development during active disease includes systemic activation of monocytes, along with probable increases in monocyte count (monocytosis).⁸

Summary

Monocytosis refers to an elevated count of monocytes, a type of white blood cell crucial for our immune system's defence mechanisms. These cells, produced in the bone marrow, play a pivotal role in identifying and eliminating pathogens, as well as supporting inflammatory responses when infections or diseases strike.

Monocytosis itself often goes unnoticed as it typically manifests as a symptom of underlying conditions rather than as a standalone issue. Common causes include chronic infections like tuberculosis, inflammatory diseases such as rheumatoid arthritis, and certain types of cancers.

Speaking of tuberculosis, it's an infectious disease caused by Mycobacterium tuberculosis that primarily affects the lungs but can also impact other organs. It spreads through airborne droplets released when infected individuals cough, sneeze, or speak. The disease can lie dormant in the body (latent TB) or become active, causing symptoms like persistent cough, weight loss, fever, and night sweats.

The intriguing connection between monocytosis and tuberculosis lies in TB's ability to induce monocytosis a marked increase in monocyte levels in the blood. Monocytes, while crucial for initiating immune responses against TB bacteria, can also contribute to tissue damage during inflammation, highlighting the complex interplay between immune defence and disease progression.

Diagnosing both monocytosis and tuberculosis involves various tests like complete blood counts (CBC), peripheral blood smears, skin tests, blood tests, chest X-rays, and sputum examinations. These diagnostic tools are essential for pinpointing the presence of monocytosis and determining the severity and stage of tuberculosis infection.

Understanding the relationships not only sheds light on the complex workings of our immune system, but it also emphasises the need for early detection and treatment in effectively managing monocytosis-related illnesses including tuberculosis. Stay informed and proactive about your health knowledge is a potent weapon in the fight against diseases like these.