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blood differential

Alternative 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, 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 After the needle is withdrawn, the puncture site is covered with a bandage for a short time to prevent bleeding.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.

  • A higher percentage of neutrophils may indicate acute infection, eclampsia, gout, myeloid leukaemia, rheumatoid arthritis, rheumatic fever, acute stress, thyroiditis or trauma.
  • A lower percentage of neutrophils may indicate aplastic anaemia, bacterial infection, chemotherapy, influenza or radiation therapy.
  • 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 percentage of lymphocytes lower than normal may indicate chemotherapy, HIV infection, leukaemia, radiation therapy or sepsis.
  • 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.
Reviewer: eknowhow Medical Review Panel
Editor: Dr John Hearne
Last Updated: 18/09/2004
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.


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