White Blood Cell Count

What is a white blood cell (WBC) count?

Healthy blood contains a certain percentage of white blood cells (WBCs, leukocytes or leucocytes) which, as part of the body’s immune system, help the body fight infection.[1] A white blood cell (WBC) count measures the amount of white blood cells in a sample of a person’s blood. The number of white blood cells in the body differs between individuals or at different ages in their lives. The normal range for a white blood cell count in a healthy adult is between 4,000 and 11,000 WBCs per microliter (mcL) or cubic millimeter (mm3) of blood, though this may differ between males and females, and healthy children and young people usually have more.

To measure the number of white blood cells in a person’s body, a doctor will order a white blood cell count, often as part of a complete blood count (CBC) test. A low white blood cell count can indicate conditions including infections, inflammation, certain cancers, HIV/AIDS, and others, making it an important diagnostic test. Aside from these conditions, a person’s white blood cell count can indicate their immune system activity, response to cancer treatment and overall health.

White blood cells (WBCs)

There are several kinds of white blood cells (WBCs), including neutrophils, eosinophils, lymphocytes, monocytes and basophils. Each variety plays a different role in protecting the body from foreign pathogens such as viruses, bacteria, fungi and parasites. White blood cells also defend the body from allergens, mutated cells, such as cancer, and foreign matter, such as splinters, and remove dead cells, old red blood cells and other debris.[2]

A white blood cell count checks both the overall levels of white blood cells in the blood, as well as the overall proportion of different types of white blood cells.

Low white blood cell (WBC) count

The threshold for a low white blood cell count (leukopenia) varies between individuals and cases, but is generally considered to be anything lower than 4,000 white blood cells per mcL of blood in an adult. A low white blood cell count can be caused by issues including:[3]

  • Viral or bacterial infection
  • Diminished bone marrow function
  • Cancer
  • Autoimmune disorders including rheumatoid arthritis and HIV/AIDS)
  • Leukemia
  • Lupus
  • Tuberculosis
  • Cancer treatment such as radiation and chemotherapy, as well as other medications
  • Aplastic anemia

A low white blood cell count may cause symptoms such as fever, chills, headache and bodyache.

High white blood cell (WBC) count

Though it varies between individuals, a high white blood cell count (leukocytosis) is usually considered to be anything above 11,000 cells per mcL of blood in an adult. This can be related to:[4]

  • Infection
  • Bone marrow disease
  • Medications
  • Autoimmune disorders such as rheumatoid arthritis
  • Leukemia
  • Allergies
  • Tuberculosis
  • Whooping cough
  • Myelofibrosis
  • Stress
  • Smoking[5]

In most instances, there are no specific symptoms related to an elevated white blood cell count, though symptoms associated with the underlying medical condition may occur. However, in extreme cases, such as when leukocytosis occurs because of a condition affecting the bone marrow, symptoms directly related to an elevated white blood cell count may occur.

Test procedure

To carry out a white blood cell count, a doctor will draw a blood sample, usually from a vein in the arm or the back of the hand. This is a common procedure, and side effects are rare, but may include lightheadedness, bleeding or infection. No special preparation is required for a white blood cell count, but a person should inform their doctor of any medications they are taking, as these can affect the results. A white blood cell count is usually taken as part of a complete blood count.

FAQs

Q: What is a healthy white blood cell (WBC) count?
A: For an adult, a healthy WBC count is considered to be between 4,000 and 11,000 WBCs per microliter (mcL) of blood. This is on average – some healthy individuals may have a higher or lower count.

Q: What is leukocytosis?
A: Leukocytosis is the condition of having an abnormally high WBC count. In most cases, an elevated WBC count will result in no symptoms, though symptoms associated with the underlying condition causing the high WBC count may occur. In extreme cases, such as when leukocytosis occurs because of a bone marrow disorder, symptoms directly related to an elevated WBC count may occur.

Q: What is hematology?
A: Hematology (alternatively spelled haematology) is the branch of medicine concerned with blood and the various disorders and conditions involving blood. This includes the study of problems with white blood cells (WBCs), red blood cells (RBCs), bone marrow and platelets, which may include conditions such as anemia, leukemia, myeloproliferative disorders and neutropenia.[6]

Q: Are there any types of cancer associated with white blood cells (WBCs)?
A: Yes, there are two main types of cancer associated with WBCs: leukemia and lymphoma. Leukemia is a cancer found in the blood and bone marrow which is caused by the rapid production of abnormal WBCs. These abnormal cells impair the body’s ability to fight infection, as well as the ability of bone marrow to produce platelets and red blood cells.[7] There are four main types of leukemia: acute myeloid, chronic myeloid, acute lymphocytic and chronic lymphocytic. Lymphoma, the second type of cancer involving WBCs, occurs when lymphocytes (small leukocytes that are part of the immune system) behave abnormally and collect in certain areas of the body. Lymphocytes can collect anywhere in the body, most commonly in the lymph nodes in the neck, armpits and groin.[8] Treatment options are available for both types of cancer.

Q: What is the relationship between bone marrow and white blood cells (WBCs)?
A: Bone marrow is the soft tissue inside the bones. It contains stem cells which can develop into WBCs, RBCs and platelets.[9]


  1. Health Library: Facts About Blood.” Johns Hopkins Medicine. Accessed: 16 September, 2017

  2. Health Library: Facts About Blood.” Johns Hopkins Medicine. Accessed: 16 September, 2017

  3. Low White Blood Cell Count.” Mayo Clinic. Accessed: 16 September, 2017

  4. High White Blood Cell Count.” Mayo Clinic. Accessed: 16 September, 2017

  5. Vital Health and Statistics: Total White Blood Cell Counts for Persons Ages 1-74 Years With Differential Leukocyte Counts for Adults Ages 24-74 Years: United States 1971-75.” Centers for Disease Control and Prevention. Accessed: 16 September, 2017

  6. Blood Disorders.” American Society of Hematolog. Accessed: 3 May, 2018.

  7. “[Blood Cancers.] (http://www.hematology.org/Patients/Cancers/)” American Society of Hematology. Accessed: 3 May, 2018.

  8. What is lymphoma?” Bloodwise. Accessed: May 3, 2018.

  9. Bone Marrow Diseases.” Medline Plus. Accessed: May 3, 2018.