T cells are a type of white blood cells (lymphocytes). They make up part of the immune system. T cells help the body fight diseases or harmful substances.
A test can be done to measure the number of T cells in your blood.
Alternative NamesThymus derived lymphocyte count; T-lymphocyte count
How the test is performedBlood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.
Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
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 testNo special preparation is necessary.
How the test will feelWhen 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 performedYour doctor may order this test if you have signs of an immunodeficiency disorderor a disease of the lymph nodes. It is also used to monitor how well therapy for these types of diseases is working.
Normal ValuesNormal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What abnormal results meanHigher than normal T-cell levels may be due to:
Lower than normal T-cell levels may be due to:
Risks associated with having blood drawn are slight:
Note: This test is often performed on people with altered immune systems. Therefore, the risk for infection may be somewhat greater than when blood is drawn from a person with a normal immune system.
Special considerationsThis following can affect test results:
Bagby GC. Leucopenia and leukocytosis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 173.
T cells are a type of white blood cells called lymphocytes. They make up part of the immune system. T cells help the body fight diseases or harmful substances.
A test can be done to measure the number of T cells in your blood.
Alternative NamesThymus derived lymphocyte count; T-lymphocyte count
How the test is performedA 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 testNo special preparation is necessary.
How the test will feelWhen 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 performedYour doctor may order this test if you have signs of an immunodeficiency disorderor a disease of the lymph nodes. It is also used to monitor how well therapy for these types of diseases is working.
Normal ValuesNormal 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.
What abnormal results meanHigher than normal T-cell levels may be due to:
Lower than normal T-cell levels may be due to:
Risks associated with having blood drawn are slight:
Note: This test is often performed on people with altered immune systems. Therefore, the risk for infection may be somewhat greater than when blood is drawn from a person with a normal immune system.
Special considerationsThis following can affect test results:
Berliner N. Leukocytosis and leukopenia. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 116.
Reviewed ByReview Date: 08/20/2011
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.
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