A blood sample is needed. For information on how this is done, see: Venipuncture
In the laboratory, the white blood cells (including T cells) are separated from the other blood cells. A stain or other substance that "labels" the cells is added to the sample to help identify which type of white blood cells are present.
How to prepare for the test
No special preparation is necessary.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
Your doctor may order this test if you have signs of an immunodeficiency disorder or a disease of the lymph nodes. It is also used to monitor how well therapy for these types of diseases is working.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
Berliner N. Leukocytosis and leukopenia. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 116.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.