White Blood Count (WBC)
Reviewed
Also called: WBC count, White blood cell count
A white blood count measures the number of white blood cells (WBCs) in your blood. White blood cells, also called leukocytes, are part of your immune system.
Specimen: Blood
Why this test may be ordered
- To help diagnose or monitor disorders related to a high or low white blood cell count
- If you have signs of infection, inflammation, or autoimmune disease
- To monitor treatment if you have a disease that weakens your immune system or take medicine that lowers your immune response
- As part of a routine screening for newborns or children with symptoms of a white blood cell disorder
Preparation and collection
You don't need any special preparations for a white blood count. You may need to stop taking certain medicines before this test, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. To test children, a health care provider will take a sample from the heel (newborns and young babies) or the fingertip or arm (older babies and children).
After a blood test, you may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly. There is very little risk to your baby or child with a needle stick test.
Understanding results
Your provider will consider your symptoms, medical history, and the results of other blood tests to understand your white blood count results.
What does a high white blood cell count mean?
High white blood count (leukocytosis): Conditions that may cause a high white blood count, also called leukocytosis, include: An infection, An inflammatory disease such as rheumatoid arthritis, An allergy, Leukemia or Hodgkin disease, Tissue damage from a burn injury or surgery. Limitation: Smoking, stress, a reaction to a medicine, or pregnancy may also cause your body to make more white blood cells, which leads to a high white blood count. Next step: White blood count results are often compared with results of other blood tests, including a blood differential.What does a low white blood cell count mean?
Low white blood count (leukopenia): Conditions that may cause a low white blood count, also called leukopenia, include: Bone marrow damage. This may be caused by infection, disease, or treatments such as chemotherapy. Cancers that affect the bone marrow. An autoimmune disorder, such as lupus. Limitation: Certain medicines, including chemotherapy, may also lower the number of your white blood cells. Next step: If you have questions about your results, talk to your provider.
- A white blood count can show if the number of your white blood cells is too high or too low, but it cannot confirm a diagnosis.
- Results are usually interpreted along with other tests, such as a complete blood count, blood differential, blood smear, or bone marrow test.
- Certain medicines, smoking, stress, and pregnancy can affect your white blood count.
- Your provider will consider your symptoms and medical history when interpreting results.
What to do next
If you are already being treated for a white blood cell disorder, your results may show if your treatment is working or whether your condition has improved. If you have questions about your results, talk to your provider.
- What is a white blood count and what does it measure?
- Why might I need this test?
- How is the blood sample collected?
- Do I need to do anything to prepare for the test?
- What do the results mean and what are the next steps?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.