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Alternative Names Return to topThymus derived lymphocyte count; T-lymphocyte count
Definition Return to top
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.
How the Test is Performed Return to top
Blood 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 Test Return to top
No special preparation is necessary.
How the Test Will Feel Return to top
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 Return to top
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 Results Return to top
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean Return to top
Higher than normal T-cell levels may be due to:
Lower than normal T-cell levels may be due to:
Risks Return to top
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.
Considerations Return to top
This following can affect test results:Update Date: 10/15/2007 Updated by: Frank A. Greco, M.D., Ph.D., Director, Biophysical Laboratory, The Lahey Clinic, Burlington, MA. Review provided by VeriMed Healthcare Network.