Your blood is made up of red blood cells, white blood cells, platelets, and plasma. White blood cells only make up about 1% of your blood, but they have an important function. As part of your immune system, they protect you against illnesses.
Monocytes are one of the five different types of white blood cells. The others are lymphocytes, basophils, neutrophils, and eosinophils.
What Are Monocytes?
Monocytes are a type of white blood cell. White blood cells are an important part of your immune system. Like the other types of white blood cells, monocytes are produced in your bone marrow and then enter your bloodstream. After a few hours, monocytes move from your blood into your lung, liver, or spleen tissue where they develop into macrophages. These are scavenger cells that fight certain infections, destroy cancer cells, and help other white blood cells remove dead or damaged tissues.
Monocytes are one of the five different types of white blood cells. The others include:
- Lymphocytes, which create antibodies to fight against viruses and bacteria
- Basophils, which secrete chemicals such as histamine to help your body's immune response
- Neutrophils, your body's first line of defense, are the most numerous among white blood cells. They kill bacteria and fungi
- Eosinophils, which help with your body's allergic response and kill cancer cells and parasites
How are Monocytes Measured?
To measure your monocyte levels, your doctor will test a sample of your blood.
Complete blood count (CBC) with differential
This blood test measures several components of your blood. You might also hear it called a full blood count or blood cell count. Your doctor may order one as part of your routine physical or to see if you have an infection or other condition, such as anemia.
A complete blood count measures:
- Red blood cells, which carry oxygen from your lungs to other parts of your body
- Hemoglobin, the protein in your red blood cells that carries oxygen.
- Hematocrit, which shows how much of your blood is made of red blood cells
- Mean corpuscular volume (MCV), a measure of the average size of your red blood cells
- Platelets, the cells that help your blood clot and stop bleeding
- White blood cells, which fight infections and other diseases
The blood differential test tells your doctor the count of each of the five types of white blood cells. It also tells if the different types of white blood cells are in normal proportion to each other, if there are more or less of them than normal, and if any abnormal or immature white blood cells are present.
Absolute monocyte count
- An absolute monocyte count tells how many monocytes are in your blood. To get it, the lab multiplies the percentage of monocytes from your complete blood count by the total number of white blood cells in your blood. This number tells your doctor if your monocyte count is normal, too high, or too low.
A CBC with differential is done by collecting a sample of your blood from a vein in your arm into a tube. Unless your doctor has ordered other blood tests at the same time, you usually do not need any special preparation for this test. Your doctor will tell you if you need to fast before these tests.
Normal Monocyte Range
In healthy people, monocytes make up about 1%-9% of total white blood cells. You might see this reported as an absolute monocyte count in the range of 0.2-0.6 × 109 monocytes per liter of blood. Ask your doctor if you need help interpreting test results.
The complete range of normal white blood cells includes:
- Neutrophils: Between 55% and 70% of total white blood cells
- Lymphocytes: Between 20% and 40% of total white blood cells
- Monocytes: Between 2% and 8% of total white blood cells
- Eosinophils: Between 1% and 4% of total white blood cells
- Basophils: Between 0.5% and 1% of total white blood cells
High Monocyte Count
Monocytosis
A monocyte count that is higher than the normal range is called monocytosis. In medical terms, monocytosis is when your absolute monocyte count is greater than or equal to 1 × 109 monocytes per liter of blood.
Monocytosis doesn't usually cause symptoms. If you do have symptoms, they'll usually be from whatever is causing your high monocyte count.
High monocyte count causes
High monocyte count is most often linked to long-term infections, blood disorders, or autoimmune conditions.
Some causes of monocytosis include:
- Short-term or long-term infections, including viral infections such as COVID-19 or mononucleosis or bacterial infections such as tuberculosis
- Blood disorders, such as sickle cell disease or hemolytic anemia
- Autoimmune or inflammatory disorders such as inflammatory bowel disease, sarcoidosis, and lupus
- Short-term or long-term stress. Intense exercise can cause a temporary high monocyte count and so can emotional stress.
- Reaction to some medications, such as steroids
- Pregnancy
- Splenectomy (removal of your spleen)
- In some cases, certain types of cancer, especially leukemias and lymphomas
How to treat monocytosis
Monocytosis itself is only a sign, so, your treatment will depend on what's causing it. Your doctor may do tests to help determine the cause of your monocytosis. Once that's determined, they'll give you appropriate treatment if needed.
Low Monocyte Count
Monocytopenia
A monocyte count that's lower than the normal range is called monocytopenia. Monocytopenia is when your absolute monocyte count is less than or equal to 0.5 × 109 monocytes per liter of blood.
If you have symptoms with monocytopenia, they're usually from whatever caused your low monocyte count.
Low monocyte count causes
You can have a low monocyte count because of some conditions, medical treatments, or injuries that lower your total white blood cell count. These include:
- Infections, such as Epstein-Barr virus, adenovirus, or HIV
- Bloodstream infections, such as bacterial sepsis
- Taking steroids or immunoglobulin therapy
- Cancer treatments, such as chemotherapy or radiation therapy)
- Surgery on your stomach or intestines
- Hemodialysis
- A genetic condition called GATA2 deficiency
- Bone marrow disorders, such as aplastic anemia
- Burn injuries
- Certain cancers, especially leukemias and lymphomas. These may include hairy cell leukemia and acute lymphoblastic leukemia or Hodgkin's lymphoma
How to treat monocytopenia
You don't need treatment for monocytopenia itself. Your doctor may do tests to figure out what's causing it and treat that if needed.
If a medical treatment causes your low monocyte count, your doctor may change your dose or the time you take your medication. Never stop or change your medications without talking to your doctor first.
If your low monocyte count is caused by an underlying condition or infection, your doctor will treat it.
If you have low levels of vitamins that are important for your immune system function (such as vitamins B12, C, or D), your doctor may recommend vitamin supplements.
Improving Monocyte Function
You may be able to improve your monocyte function with a healthy lifestyle. For instance:
- Eat a well-balanced diet.
- Exercise regularly.
- Reduce or manage your stress.
- Don't smoke.
- Use alcohol in moderation.
- Protect yourself against infections by washing your hands often and avoiding contact with people who are sick.
If your monocyte count is high or low because of a health condition or medication, follow your doctor's instructions.
Your doctor may be able to suggest other ways to improve your immune function, such as vitamin supplements.