Posted September 13, 2022 by Anusha ‐ 4 min read

Monocytes are a type of white blood cell in your immune system. Monocytes turn into macrophage or dendritic cells when an invading germ or bacteria enters your body. The cells either kill the invader or alert other blood cells to help destroy it and prevent infection.

What are monocytes?

Monocytes are a type of white blood cell (leukocytes) that reside in your blood and tissues to find and destroy germs (viruses, bacteria, fungi and protozoa) and eliminate infected cells. Monocytes call on other white blood cells to help treat injury and prevent infection.

What are the functions of monocytes?

  • Monocytes are your cell’s firefighters. Their lifecycle begins in the bone marrow (soft tissue inside of your bones) where they grow and train to protect your body.

  • Once they mature, they enter your bloodstream and tissues to defend your body against foreign invaders, like germs.

Germs are similar to fires when they enter your body. Once germs are inside your tissues, monocytes hear an alarm, calling them into action to fight the fire. These cellular firefighters differentiate into two types of cells:

Dendritic cells

  • Ask other cells in your immune system for backup to fight germs.

  • Dendritic cells are your fire department’s call center.

  • They’re responsible for alerting other cells in your body to help fight infection. Dendritic cells reside in superficial tissues, such as just beneath your skin and in the lining of your nose, lungs, stomach and intestine.

  • When a germ enters the body’s tissues, dendritic cells collect the antigen of the invading germ (the molecule in the germ that produces an antibody response) and release proteins (cytokines) that notify other white blood cells to come to the site of the infection and destroy the invader.


  • Defend your body from germs on the front lines.

  • Macrophages are on the front lines of the fire, fighting germs (viruses, bacteria, fungi and protozoa) that enter your body.

  • Macrophage cells surround the invading germ and ingest and kill it with toxic enzymes within the cell.

  • These cells also help remove dead cells from your tissues and bloodstream.

Where are monocytes located?

Monocytes form in the soft tissue of your bones (bone marrow). After the cells mature, they travel to your tissues where they defend your body from infection alongside other cells in your immune system.


Monocytosis occurs when your monocyte count is too high. It’s most often linked to a chronic infection or disease that your body is fighting. Causes of monocytosis include:

  • Autoimmune diseases (lupus, rheumatoid arthritis).

  • Blood disorders.

  • Cancer (leukemia, lymphoma).

  • Cardiovascular disease.

  • Infection (mononucleosis).

  • Inflammatory disorder (sarcoidosis).


Monocytopenia occurs when your monocyte count is too low. This is the result of decreases in your white blood cell count. Causes of monocytopenia include:

  • Aplastic anemia.

  • Blood infection.

  • Burn injuries.

  • HIV.

  • Reaction to chemotherapy.

What is a normal range for my monocyte count?

A normal monocyte count is between 2% and 8% of your white blood cell count. This equals about 200 to 800 monocytes per microliter of blood in healthy adults. If your monocyte count is outside those ranges, you’re at risk of acquiring a monocyte-related condition.

What are common tests to check the health of my monocytes?

A blood test checks the health of your monocytes. Two tests specifically identify how many monocyte cells are in your body:

  • Complete blood count: Your healthcare provider will draw a sample of your blood from your vein to diagnose and screen for several conditions and infections by counting your blood cells. Since monocytes are a type of white blood cell, your healthcare provider will request a complete blood count (CBC) with differential. This test counts the five types of white blood cells in your blood sample to verify whether or not your cell count is normal, too high or too low.

  • Absolute monocyte count: An absolute monocyte count identifies how many monocytes are present in a sample of your blood. The calculation for an absolute monocyte count multiplies the percentage of monocytes from a complete blood count by the total number of white blood cells from the same count. The results from this test identify whether or not your monocyte count is normal, too high or too low.

What are common treatments for monocyte conditions?

  • Treatment is dependent on your diagnosis and the severity of your condition.

  • It could be as simple as changing your diet or as significant as treating an underlying condition with chemotherapy.

  • Your healthcare provider will offer treatment options specific to your diagnosis to help you decide on the best way to either increase or decrease your monocyte count.

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