Blood Differential

Alternate Names : White Blood Cell Differential Count, Differential

The blood differential test measures how many different kinds of white blood cells are in the bloodstream. It tests to see if the structure of the white blood cells is normal or abnormal.

Who is a candidate for the test?

This test is ordered to check for infection, anemia or leukemia. It can also be used to monitor the course of treatment in these conditions.

How is the test performed?

A blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, or "tourniquet," is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle, and is collected in a syringe or vial. After the needle is withdrawn, the puncture site is covered with a bandage for a short time to prevent bleeding. In the laboratory, a drop of the blood is placed on a microscope slide. A blood smear is made and stained. A person trained in performing blood counts observes the slide under a microscope and performs a white blood cell differential count.