White blood cell differential count

Other names: White blood cell morphology; Diff; Differential leucocyte count; WBC differential

White blood cells are the body’s natural defence mechanism; they help to fight off infection and assist the immune system; they are made in the lymphoid system and the bone marrow. There are five forms of white blood cell; these are lymphocytes, neutrophils, monocytes, basophils and eosinophils. The differential test helps to assess the proportion of each type of white blood cell in relation to the other types of white blood cell.

When is the test used?

The white blood cell differential test is used to test the body’s ability to respond to and combat infection; it can also be used to detect certain types of leukaemia and lymphoma. The test is usually ordered as part of the full blood count test, which measures all the different types of cell within the blood. The differential test may also be used to determine the severity of allergies and parasitic infections.

How is the test performed?

The test is done by analysing a sample of blood; in most cases, the sample is taken from a vein in the arm, but in young children it may be taken from the finger or the heel (this is done by pricking the heel or finger and collecting the blood). A needle is inserted into the vein (usually on the inside of the elbow) and the blood is drawn out and collected in a syringe; once the sample has been collected, it will bottled and labelled with the patient’s name before being sent away to the laboratory for analysis.

What do the test results mean?

The results of the differential test indicate the proportions of each type of white blood cell; differences in the levels of cells may indicate different conditions, as follows:

  • Neutrophils: levels may increase in response to a bacterial infection, an inflammatory condition or leukaemia (this is much rarer); steroid medications may also cause levels to rise. Decreased levels may indicate a severe infection; chemotherapy treatment also causes levels of neutrophils to fall.
  • Basophils: levels may increase as a result of leukaemia, long-term inflammation or a severe, hypersensitive reaction to a type of food; radiation therapy may also cause levels to rise.
  • Eosinophils: levels increase as a result of parasitic infections, allergic reactions and inflammation of the skin. Malignancies which affect the bone marrow may also cause levels to rise.
  • Monocytes: increased levels may be seen in some cases of leukaemia, as well as general infections and inflammatory conditions. Decreased levels may indicate problems with the bone marrow.
  • Lymphocytes: increased levels may indicate viral or bacterial infections, lymphoma or leukaemia; radiation therapy may also cause levels to rise. Decreased levels may be caused by stress, HIV and lupus.

White blood cell levels may be affected by diet, physical exercise and stress.

Specific Blood Tests

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