Alternative Names white blood cell differential count, differential
Definition 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, anaemia or leukaemia. 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 After the needle is withdrawn, the puncture site is covered with a bandage for a short time to prevent bleeding.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.
What is involved in preparation for the test? Specific instructions are available from a doctor.
What do the test results mean? There are different types and amounts of white blood cells. The different white blood cells play different roles. The cells are found in the blood at normal, healthy levels. Some destroy foreign cells and organisms. Some make antibodies that attack cells that are infected with a virus. Some destroy unwanted cells and organisms. Some help improve the permeability of capillaries.
The different types of white blood cells include neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
An increased percentage of lymphocytes may indicate chronic bacterial infection, infectious hepatitis, infectious mononucleosis, lymphocytic leukaemia, multiple myeloma, viral infection or recovery from a bacterial infection.
A higher percentage of monocytes may indicate chronic inflammatory disease, parasitic infection, tuberculosis or viral infection.
An increased percentage of eosinophils may indicate allergic reaction, parasitic infection or Hodgkin's disease.
A decreased percentage of basophils may mean acute allergic reaction.
Author: Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 18/09/2004 Contributors Potential conflict of interest information for reviewers available on request
