White Blood Cell Differential: About This Test

What is it?

A white blood cell differential counts the different types of white blood cells in a blood sample. There are five major kinds of white blood cells. The numbers of each type of white blood cell give important information about your immune system.

Why is this test done?

The test helps to measure how the body is responding to different types of infections. It can also help measure certain allergic reactions. It can sometimes be helpful in finding the stage of leukemia or how the body is responding to chemotherapy.

How do you prepare for the test?

In general, there's nothing you have to do before this test, unless your doctor tells you to.

How is the test done?

A health professional uses a needle to take a blood sample, usually from the arm.

Your doctor may order a blood smear test to be done at the same time. In this test, a drop of blood is smeared on a slide and stained with a special dye. The slide is looked at under a microscope. The number, size, and shape of red blood cells, white blood cells, and platelets are recorded. Blood cells with different shapes or sizes can help diagnose many blood diseases, such as leukemia, malaria, and sickle cell disease.

How long does the test take?

This test will take a few minutes.

What happens after the test?

• You will probably be able to go home right away.
• You can go back to your usual activities right away.