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White Blood Count (WBC)
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

White Blood Count (WBC)

A white blood count measures the number of leukocytes in your blood to help diagnose or monitor infections, inflammation, and immune system disorders.

What is a white blood count (WBC)?

A white blood count measures the total number of white blood cells (WBCs) in your blood. These cells are produced in your bone marrow and are a vital part of your immune system. When you are sick or injured, your body produces more WBCs to fight off bacteria, viruses, or other foreign substances. Conversely, certain diseases or medications can lower your WBC count.

There are five major types of white blood cells:

  • Neutrophils
  • Lymphocytes
  • Monocytes
  • Eosinophils
  • Basophils

What is it used for?

The test is used to help diagnose or monitor conditions related to high or low WBC counts:

  • High WBC count (leukocytosis): May indicate autoimmune/inflammatory diseases, infections, cancers like leukemia or Hodgkin disease, or allergic reactions.
  • Low WBC count (leukopenia): May indicate immune system diseases (like HIV), lymphoma, or liver/spleen diseases.

Why do I need a white blood count?

You may need this test if you have symptoms of infection, such as fever, chills, body aches, or a wound that won't heal. It is also used if you have a condition that weakens your immune system or if you are taking medications that affect your immune response.

What do the results mean?

Results are interpreted alongside your symptoms and medical history. A high count can be caused by infection, inflammation, stress, smoking, or pregnancy. A low count may be caused by bone marrow damage, certain cancers, or autoimmune disorders like lupus.

Is there anything else I need to know?

WBC results are often compared with a blood differential, which measures the amount of each specific type of white blood cell. For example, neutrophils primarily target bacterial infections, while lymphocytes target viral infections.

Frequently Asked Questions

During chemotherapy, a WBC (especially neutrophil) count below 1,000 cells/µL is considered neutropenic and raises infection risk. You should contact your oncology team promptly if you develop fever, chills, sore throat, cough, or any new skin breakdown. Many practices have a “fever‑and‑neutropenia” protocol that may include same‑day evaluation and empiric antibiotics.
Yes. Physical stress (heavy exercise, heat exposure) and emotional stress trigger the release of cortisol and catecholamines, which can increase circulating neutrophils and raise the total WBC for several hours. This is a normal physiological response and usually resolves without intervention.
No special fasting is required for a basic CBC with WBC. However, certain medications (e.g., chemotherapy, steroids, immunosuppressants) can affect the count, so inform the lab or your provider about all drugs you’re taking. Some clinicians ask patients to avoid vigorous exercise for 24 hours before the draw because intense activity can temporarily raise neutrophils.
mild, isolated elevation often reflects a transient response to stress, recent infection, smoking, or even vigorous exercise. In most asymptomatic adults, clinicians will repeat the count in a few weeks to see if it normalizes before initiating any treatment. If the elevation persists or is accompanied by symptoms (fever, night sweats, unexplained weight loss), further evaluation for infection, inflammation, or hematologic disorders may be warranted.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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