High White Blood Cell Count, Explained

When you're sick, your body makes more white blood cells than usual. That means a high white blood cell count could indicate that you have some sort of illness.

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White blood cells—which are also called leukocytes—protect the body against infection from invading organisms like viruses, bacteria, and parasites. Designed to identify and destroy pathogens, white blood cells are found in both the body’s tissues and bloodstream.

A high white blood cell count indicates that something like an infection, allergic response, or inflammation is happening inside your body. That’s because when you get sick, your body makes more white blood cells to fight whatever is causing your illness. Exercise, pregnancy, and even certain medications can also cause your white blood cells to be elevated.

Because a high white blood cell count, or leukocytosis, might be a sign of an underlying condition, it’s important to figure out what’s causing the elevation and address that condition.

What Are White Blood Cells?

White blood cells are a type of blood cell that are made in your bone marrow and found in your bloodstream and tissues. They are an integral part of your immune system and help your body fight infections and diseases.

Overall, there are five different types of white blood cells, each with a different role. Analyzing which of your white blood cells are high could help healthcare providers pinpoint what’s at the root of your issue. Here is an overview of the different types of white blood cells and their functions in the body.


Neutrophils are the most abundant white blood cell in the body, representing 70% of your white blood cell population. Considered a first line of defense for your immune system, neutrophils are designed to attack and kill invaders like bacteria and fungi. Billions of these cells are released from your bone marrow each day, but they do not live long. They do their job and then are replaced by fresh neutrophils all within just a few hours.


While eosinophils play a role in fighting infections, their primary role is attacking and killing parasites. These white blood cells, which represent about 5% of your white blood cells, also play a role in allergic responses. But sometimes, eosinophils can overreact to a foreign invader like pollen and mount a significant allergic response. 


Basophils quickly release a chemical known as histamine when you come into contact with something to which you’re allergic. Histamine is a common marker of an allergic reaction and impacts the body’s immune response. It also can be the root behind anaphylaxis and hypersensitivity.


These white blood cells come in two forms—B cells and T cells—and are sometimes called your memory cells because they create antibodies to fight against viruses, bacteria, and other harmful invaders. 

More specifically, your T cells directly fight foreign invaders and produce cytokines, which are biological substances that activate other parts of your immune system. Meanwhile, B cells produce antibodies that remember an infection and are on guard in case your body is exposed to that pathogen again.


With one of the longest lifespans of any of your white blood cells, monocytes’ primary roles are to break down bacteria and clean up dead cells in the body. About 5% to 12% of the white blood cells in your bloodstream are monocytes.

What Is Considered a High White Blood Cell Count?

Unless you have a known illness or disease that your healthcare provider is monitoring, your white blood cell count is usually done as part of a routine physical exam. During the exam, your practitioner will order a blood test called a complete blood count, which measures different parts of your blood including your white blood cells.

While some labs will use slightly different ranges for the white blood cell tests, the Leukemia and Lymphoma Society suggests that the following counts are the normal ranges for white blood cells:

 Population  White Blood Cells Per Microliter of Blood
Men 5,000 to 10,000
Women 4.500 to 11,000
Children 5,000 to 10,000

A high white blood cell count, or leukocytosis, is anything that exceeds the normal range for your demographic.

What Causes a High White Blood Cell Count?

A high white blood cell count usually indicates that some sort of change is taking place inside your body. If your blood test results come back with an elevated white blood cell count, your healthcare provider will investigate to determine the exact cause. 

Sometimes, the high count can be a sign of cancers like leukemia or Hodgkin disease. But there are many other reasons why your white blood cell count can be high—and not all the reasons are related to being sick. 

The following can cause your white blood cell count to be high:

  • An infection (viral or bacterial)
  • Inflammation
  • Severe emotional stress
  • Severe physical stress, such as fever, injury, or surgery
  • Burns
  • Kidney failure
  • An autoimmune disease like rheumatoid arthritis or lupus
  • Malnutrition
  • Thyroid problems
  • Certain medications
  • Allergic reactions
  • Viruses
  • Smoking 
  • Intense exercise

People who are pregnant can also have higher white blood cell counts because of the stress their changing bodies go through. These white blood cell counts usually return to normal a few weeks after their baby is born, though.

Signs and Symptoms of High White Blood Cells

Elevated white blood cells on their own do not cause any symptoms. However, you may experience symptoms of the condition causing the high levels.

For instance, if your white blood cell count is high from an allergic reaction, you might have a rash or hives.

If the count is high from an infection, you might experience fever, chills, body aches, and headache.

How Is a High White Blood Cell Count Treated?

Getting your white blood cell count back to normal range will mean treating whatever is causing the higher levels. That means treatment can vary widely since the cause of high white blood cell counts vary widely. For example, if you have a bacterial infection like a urinary tract infection or pneumonia, then your healthcare provider may prescribe antibiotics. 

Other treatments for causes of high white blood cell count include:

  • Antihistamines for allergic reactions
  • Steroids or immunosuppressants for autoimmune diseases or inflammatory disorders 
  • Medications to manage or treat stress
  • Anti-inflammatory medications to manage inflammation
  • Chemotherapy, stem cell therapies, or radiation to treat cancer
  • Medications to lower or procedures to remove the white blood cells in your blood if you have chronic myeloid leukemia

When to See a Healthcare Provider

Seeing a healthcare provider on a consistent basis is important for preventative healthcare. During these regular visits, your provider will often order routine blood work that can help identify any potential issues early on.

In the meantime, if you suspect that you have developed an infection, allergy, or inflammation, you should reach out to a healthcare provider, especially if you experience a fever that will not go down or go away, shortness of breath, a cough that lasts more than two weeks, or symptoms that last more than 10 days.

Some other indicators that you should see a healthcare provider include:

  • Irregular or rapid heart rate
  • Dizziness
  • Unexplained weight loss
  • Fatigue that won’t go away
  • Severe sweating or cold sweats
  • Swelling in the ankles or legs
  • Unexplained rashes or spots
  • Swollen, red, or tender joints

A healthcare provider will determine whether your symptoms call for blood work that includes a white blood count test.

If you have already been diagnosed with a disease or illness that involves a high white blood cell count—like leukemia or an autoimmune disease—your provider has likely told you when to reach out with issues. If you have any new concerns, you can always reach out to your provider.

A Quick Review

White blood cells are an integral part of your immune system. The cells help fight pathogens like viruses and bacteria.

When your white blood cells are actively fighting against foreign invaders, you will likely have a high white blood cell count. This measurement—taken through a blood test—can be an indicator of an issue like an infection, disease, or allergic reaction.

Based on any symptoms you might have, your provider may run additional tests or blood work to make a diagnosis and develop a treatment plan.

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