White Blood Count (WBC)
Reviewed
A white blood count measures the number of white blood cells (WBCs) in your blood. White blood cells are part of your immune system and help fight infections and other diseases.
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.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- 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 have questions about your results, talk to your provider. Your provider will consider your symptoms, medical history, and the results of other blood tests to understand your white blood count results and determine if any follow-up is needed.