It can indicate recovery from a health problem

Leukocytosis is the condition of having a high number of leukocytes in the blood. Leukocytes are white blood cells. They include many different white blood cell types that all work together and have specific roles in immunity, healing, and maintaining health.

Leukocytosis may be a temporary response to an infection or injury as the body is healing naturally, or it can be a sign of disease. It may develop as a side effect of some medications, or it may reflect an underlying autoimmune disease.

Leukocytosis can involve all types of white blood cells or just a few. The effects will depend on which type of white blood cell is affected. 

A woman is checked for fever at a clinic

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Symptoms of Leukocytosis

Leukocytes have many effects on the body. Normally, these cells travel throughout the bloodstream, and they are also present in the lining of many organs, such as the intestines. They recognize infectious pathogens, like viruses and bacteria, and they activate the immune response to fight infections.

Leukocytes are directed to areas of the body that have been harmed by injury or disease, and they help repair these damaged tissues and organs. 

While a person may be totally healthy and experience physiological leukocytosis (an increase in the number of circulating leukocytes) in response to extreme physical activity or environmental stress, most cases of leukocytosis are secondary to a medical condition or medication.

Leukocytes respond to underlying medical conditions, which activate defense mechanisms in the body to help fight off infection or protect the body. It is also possible for an underlying condition to cause persistent leukocytosis.

Common body responses to underlying conditions causing leukocytosis include:

  • Warmth, swelling, tenderness, pain, or redness in a specific area of the body
  • Fever, sweats, chills 
  • Fatigue 
  • Loss of appetite, vomiting, diarrhea 
  • Sore throat, congestion, runny nose 
  • Itching, skin rash

Causes of Leukocytosis 

A healthy person can experience physiological leukocytosis in response to extreme physical activity or environmental stress, but most cases of leukocytosis are secondary to a medical condition or medication.

There are several different conditions that can cause leukocytosis. Infections and injuries are the most common causes in which temporary leukocytosis indicate the body is healing. Many diseases that require treatment can also cause leukocytosis.

Causes of leukocytosis include:

Leukocytosis that is caused by cancer can present with symptoms such as fever and fatigue. However, if cancer is present, leukocytes may no longer behave normally.

In addition, too many leukocytes may present their own problems, like leukostasis, in which plugs of white cells are seen in small blood vessels.

Sometimes overproduction of cancer leukocytes in the bone marrow can cause underproduction of other types of white blood cells, as well as anemia (low number of healthy red blood cells).

What Medications Cause Leukocytosis 

Leukocytosis can be a side effect of some medications. Examples include corticosteroids, beta agonists, lithium, epinephrine, and colony-stimulating factors.

If you have leukocytosis without a clear reason, make sure to ask your healthcare provider whether it could be a medication side effect, or check the labels on your medications, which may indicate this.

How to Treat Leukocytosis

Often, interventions that treat the underlying cause of leukocytosis will relieve the symptoms, but treatment can take a while to work. You may also need medical management for the symptoms of leukocytosis as your white cell count is returning to a normal level.

Treatments for symptoms of the underlying conditions associated with leukocytosis may include:

  • Antihistamines to reduce symptoms of inflammation 
  • Cold medicines to reduce sore throat, congestion, runny nose 
  • Tylenol (acetaminophen) or nonsteroidal anti-inflammatory drugs (NSAIDs) such as Advil (ibuprofen) or Aleve (naproxen) to reduce fever, swelling, and pain 
  • Steroids or other anti-inflammatory drugs to reduce inflammation

An infection might be treated with antibiotics. For blood cancers and autoimmune conditions, the treatment will be specific to the condition. Blood cancers often are treated with chemotherapy. Autoimmune conditions are treated with anti-inflammatory drugs and drugs that suppress the immune response.

Are There Tests to Diagnose the Cause of Leukocytosis? 

Leukocytosis is diagnosed with a complete blood count (CBC) and is defined as a white blood cell (WBC) count higher than 11,000 per cubic millimeter (11.0 × 109 per liter) in adults who are not pregnant.

The normal values of each type of leukocyte and the percentage of each type is standardized, but may vary slightly between different labs.

 Type of white blood cell  Percentage of total leukocyte count
 Neutrophil  40–60
 Lymphocyte  20–40
 Monocyte  2–8
 Eosinophil  1–4
 Basophil  0.5–1

The cause of leukocytosis can be determined with a medical history, physical examination, and diagnostic tests. The type of white blood cells that are increased can provide some information that your healthcare providers would use to determine the cause—such as cancer or inflammation.

Some tests used to identify the cause of leukocytosis include:

You might need to have one or more of these tests, but it’s unlikely that you would need all of them. Your healthcare provider will decide which of these you need based on a preliminary evaluation. 

Additionally, with leukocytosis, the excess white blood cells may have normal features, or they can be abnormal. With blood cancers, like leukemia, some leukocytes can have an abnormal shape and function, with especially harmful effects on the body.

When to See a Healthcare Provider 

Leukocytosis can be a normal part of healing and recovery from illness, or it can be a sign of an underlying disease that requires diagnostic testing and treatment. If you have signs and symptoms of leukocytosis that are causing discomfort or lasting more than a few days, you should call your healthcare provider for advice or make an appointment. 

Get prompt medical attention if you or your child has any of the following symptoms: 

  • Wheezing or trouble breathing 
  • Painful joint swelling
  • Painful or severe lymph node swelling 
  • Severe chills, sweats, or fever
  • Fever of unexplained origin
  • Severe vomiting or diarrhea 
  • Changes in consciousness, dizziness, or trouble concentrating
  • Unexplained weight loss
  • Change in energy level
  • Ease of bleeding from mucosal surfaces or skin

These can be signs of a rapid and potentially dangerous white blood cell reaction or a serious underlying medical condition. 


Leukocytosis is a high number of white blood cells. It can occur as a normal response to infections, injuries, and illness as the body is healing. In these situations, the symptoms can include a fever, chills, sweating, or fatigue, and will usually go away once the illness resolves.

Sometimes leukocytosis occurs with inflammatory or autoimmune conditions or cancer. Diagnostic tests can identify the type and cause of leukocytosis.

Frequently Asked Questions

Frequently Asked Questions

  • Should I try to lower my white blood cells?

    In general, it’s best to have a normal white blood cell count. So, if you have leukocytosis, you might need medication to treat the cause. But if your white blood cell count is normal, there is no need to change it.

  • Is leukocytosis a type of cancer?

    No, leukocytosis is not a type of cancer, and may be a normal physiological response. However, some blood cancers cause leukocytosis. It can be a temporary response to infections or other health problems during the healing process, as well. Leukocytosis can also be a reaction to autoimmune diseases and inflammatory conditions, like lupus and rheumatoid arthritis.

  • Does leukocytosis always cause symptoms?

    Underlying medical conditions may cause noticeable symptoms that are associated with leukocytosis, but they don't have to. Common body responses to underlying conditions associated with leukocytosis include fever, swelling, redness, itching, and rash. The symptoms of an infection or other conditions that’s triggering leukocytosis can also occur.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Flanagan B, Keber B, Mumford J, Lam L. Hematologic conditions: Leukocytosis and leukemia. FP Essent. 2019;485:17-23. PMID: 31613564

  2. UptoDate. Hyperleukocytosis and leukostasis in hematologic malignancies.

  3. Riley LK, Rupert J. Evaluation of patients with leukocytosis. Am Fam Physician. 2015;92(11):1004-11. PMID: 26760415

  4. Chabot-Richards DS, George TI. Leukocytosis. Int J Lab Hematol. 2014;36(3):279-88. doi:10.1111/ijlh.12212

By Heidi Moawad, MD
Heidi Moawad is a neurologist and expert in the field of brain health and neurological disorders. Dr. Moawad regularly writes and edits health and career content for medical books and publications.