White Blood Count (WBC)

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. They are a type of blood cell made in your bone marrow and found in your blood and lymph tissue (part of your immune system).

If you are injured or get sick, the white blood cells will travel through your bloodstream and tissues to where they are needed. There, they will help your body fight off infections and other diseases. When you get sick, your body makes more white blood cells to fight the bacteria, viruses, or other foreign substances causing your illness.

This increases your white blood count. Other diseases can cause your body to make fewer white blood cells than you need. This lowers your white blood count.

Diseases that can lower your white blood count include some types of cancer and HIV, a viral disease that attacks white blood cells. Certain medicines, including chemotherapy, may also lower the number of your white blood cells. There are five major types of white blood cells: Neutrophils; Lymphocytes; Monocytes; Eosinophils; Basophils; A white blood count measures the total number of these cells in your blood.

Another test, called a blood differential, measures the amount of each type of white blood cell.

Why this test is done

You may need this test if you have signs of an infection, inflammation, or autoimmune disease. The symptoms of an infection may include:

• Fever
• Chills
• Body aches
• Headache
• Wound that is red, has pus, or won't heal
• Ongoing cough

The symptoms of inflammation and autoimmune diseases will be different, depending on where in the body the inflammation is and the type of disease you have.

You may also need this test if you have a disease that weakens your immune system or are taking medicine that lowers your immune response. If the test shows your white blood count is getting too low, your provider may want to adjust your treatment.

Your newborn or older child may also be tested as part of a routine screening or if they have symptoms of a white blood cell disorder.

How to prepare

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.

Sample type

Blood

Other names for this test

WBC count, white cell count, white blood cell count, Leukocyte Count, WBC