Blood Differential

Why this test may be ordered

• As part of a routine checkup
• To help diagnose infections, autoimmune diseases, leukemia, or other cancers
• To monitor an existing blood disorder or related condition
• To investigate symptoms such as unusual tiredness, weakness, or unexplained bruising

Preparation and collection

No special preparation is necessary.

Blood sample from a vein in your arm.

There is very little risk. After the test, some people experience mild pain, dizziness, or bruising. These symptoms usually go away quickly.

Understanding results

This test measures the number and/or percentage of each type of white blood cell. Your provider will compare your results to reference ranges and interpret them based on your overall health.

• High: Your levels of one or more white blood cell types are higher than normal (leukocytosis). Limitation: Not all high results indicate a serious condition; factors like stress, smoking, or alcohol use can affect levels. Next step: Your provider may check for infection, inflammation, or other causes.
• Low: Your levels of one or more white blood cell types are lower than normal (leukopenia). Limitation: Low results may be temporary or due to medications and do not always require treatment. Next step: Your provider may investigate bone marrow function, medication effects, or other conditions.

• Abnormal results do not always mean you have a condition that needs medical treatment.
• Your provider will consider your symptoms, medical history, and other blood tests when interpreting results.

What to do next

Your provider may order other tests to help find the cause of abnormal results.

• How do my results compare to the reference range used by my lab?
• What do my specific white blood cell levels mean for my health?
• Do I need any follow-up testing?

Evidence source

U.S. National Library of Medicine: Blood Differential