White blood cells help your body fight inflammation and infections. A high or low white blood cell count may be associated with a number of short-term or long-term health conditions.

White blood cells, along with platelets and red blood cells, are key structures produced by your bone marrow. In particular, white blood cells play an important role in your immune system to help fight inflammation and infections.

White blood cell changes can also indicate underlying health problems. For example, higher or lower levels of white blood cells may be associated with infections, certain cancers, or inflammatory conditions.

Learn more about white blood cells, including their function, associated health problems, and possible symptoms you should consider discussing further with a doctor.

White blood cells make up a key part of your immune system that works to fight off infections and to help protect your body from cancers and other potentially harmful invaders.

These cells freely circulate in your blood, but may form in larger amounts in response to threats like viruses, bacteria, and allergens. Some white blood cells also play roles in inflammatory responses in acute injuries and autoimmune conditions.

Despite their everyday functions, white blood cells only make up 1% of your overall blood, and are far outnumbered by red blood cells.

There are five different types of white blood cells, each with varying functions in your body. These include granulocytes, such as eosinophils, basophils, and neutrophils, as well as monocytes and lymphocytes.

Consider the basic functions of each white blood cell type:

  • Eosinophils: These white blood cells help fight off parasitic infections, and may also help protect your body from allergic reactions and inflammatory responses.
  • Basophils: These cells primarily fight allergens, and can produce subsequent allergic reactions.
  • Neutrophils: These white blood cells are responsible for targeting bacterial and fungal infections, and they make up 55% to 70% of your total white blood cell count.
  • Monocytes: Unlike other white blood cells, monocytes primarily help clean up debris, such as old bacteria and cells. They communicate with other white blood cells to help your immune system recognize and address possible infections.
  • Lymphocytes: These make important antibodies, such as T-cells and B-cells. Lymphocytes also help protect your body from viral infections.

All white blood cells are produced by your bone marrow, and are then released in your bloodstream as well as lymph fluids.

White blood cells are microscopic and spherical shaped. Most range in size between 12 and 15 micrometers in diameter. Also, as their name suggests, granulocytes contain granules in their fluids that provide clues to their type of cells.

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Types pf white blood cells. Medical Illustration by Bailey Mariner

Each type of white blood cell has a slightly different nuclei structure and appearance when stained in a laboratory:

  • Eosinophils: Have two distinct parts of the nucleus (bi-lobed), and will stain either pink or red.
  • Basophils: May also contain a bi-lobed nucleus, as well as granules that will stain blue or purple.
  • Neutrophils: Contain three or five multi-lobed nuclei and will stain pale pink in color.
  • Monocytes: Contain C-shaped nuclei and will stain blue-gray in color.
  • Lymphocytes: These have spherical nuclei.

Your bone marrow produces white blood cells as part of its immune function. However, when you are sick or develop certain medical conditions, your body may produce fewer or more white blood cells than normal.

Medical conditions that affect a low white blood cell count

Medical conditions that may be associated with low white blood cell counts include:

  • Treatments for cancer: Chemotherapy and radiation therapy can kill healthy cells in your body, such as white blood cells, as well as cancerous ones.
  • Bone marrow problems: These include cancers or diseases of the bone marrow that can impair its function and ability to release new white blood cells.
  • HIV: This chronic condition attacks white blood cells, including neutrophils and lymphocytes.
  • Certain autoimmune diseases: These include lupus, which can cause low leukocyte levels.

Medical conditions that affect a high white blood cell count

When your immune system is trying to fight a virus, bacteria, or foreign substance, it may produce more white blood cells to help fight it. Possible medical conditions that can increase white blood cells counts include:

  • Allergies: An allergic reaction may increase both your basophil and eosinophil counts.
  • Blood cancers: These include Hodgkin lymphoma and leukemia.
  • Autoimmune or inflammatory diseases: These types of conditions cause your immune system to attack itself, and can cause your eosinophil count to increase.
  • Acute illnesses or infections: Your body releases more white blood cells in response to an acute infection or illness, particularly lymphocytes and neutrophils.

In all cases, treating the underlying cause will help normalize the immune system response and then subsequently reduce white blood cell counts.

Other possible factors that can increase your white blood cell levels include:

  • smoking
  • pregnancy
  • stress
  • adverse reactions to medications
  • a recent traumatic event or surgery

Symptoms of conditions related to white blood cells may vary depending on the underlying cause, such as an acute infection, or a chronic condition like cancer, HIV, or autoimmune disease. Possible signs and symptoms may include the following:

  • low-grade fever
  • chills
  • headaches
  • body aches
  • localized pain, such as joint pain in autoimmune conditions like rheumatoid arthritis (RA)
  • chronic cough
  • frequent illnesses
  • cuts and wounds that heal slower than normal

A normal white blood cell range for adults is between 4,500 and 11,000 cells per microliter (μL). The ranges tend to be higher in children, and they are based on age.

For example, 6,000 to 17,500 cells/µL is considered normal for infants younger than 1 year old, but those in children 10 years of age should be between 4,500 to 13,500 cells/μL.

Pregnant people may also have a higher range at 5,800 to 13,200 cells/µL.

A healthcare provider may order a complete blood count (CBC) to measure your white blood cells. This will also reveal red blood cell and platelet counts. A CBC is also often a first-step in diagnosing certain infections, inflammatory conditions, and cancers.

If your doctor is interested in looking at specific types of white blood cells, they will also order a blood differential test.

It’s important to note that a CBC and blood differential may be done in conjunction with other tests, such as a blood smear, in order to help make an accurate medical diagnosis.

Raising or lowering a white blood cell count depends on how out of range your test results are, as well as the underlying cause. Most people need treatment for the underlying cause, and not the blood cell counts directly.

First, if your white blood cell counts are too low, a doctor may need to treat the underlying cause, or adjust any medications you currently take.

In such cases, a doctor may need to monitor your white blood cell count on a regular basis, especially if you’re taking immunosuppressants for certain medical conditions. This will help them determine if your treatment is working, and if they need to adjust your dosage.

Some people with cancer may need medications to help offset the side effects of their treatment. One example is filgrastim (Neupogen), an injectable medication that helps your body make white blood cells after radiation treatments.

On the flipside, a white blood cell count that is too high could warrant further testing and treatment. These are signs of your body fighting an infection or invasion. Once the underlying cause is treated, your blood cell counts may go back into a normal range.

White blood cells are an integral part of your immune system. Without them, you would not be able to fight off everyday pathogens, allergens, or other inflammatory and infectious substances.

When your immune system detects a potential invader, your white blood cell count may increase. This is normal during an acute illness or injury. However, chronically high or low levels could indicate a medical issue that needs further evaluation.