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Alternative names Return to top
T cell counts; CD4 count; CD3 count; T-lymphocyte countDefinition Return to top
This is a blood test that measures the number of T-lymphocytes (a type of white blood cell).How the test is performed Return to top
Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
In the laboratory, the white blood cells are separated from the other blood cells. A stain or other substance that "labels" the cells is added to help identify which type of white blood cells are present.
B and T lymphocytes look the same under an ordinary microscope. However, they may be differentiated with an electron microscope. B or T lymphocytes may also be counted using immunofluorescence or by flow cytometry. T cells can also be differentiated by the E rosette test (Blood is mixed with sheep red blood cells. The T cells will cling to the sheep cells and produce a distinctive rosette pattern).
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
A T-cell count of may be helpful in the diagnosis of immunodeficiency diseases and lymphocytic diseases. It is also used to monitor the response to therapy for these types of diseases.Normal Values Return to top
Lymphocytes make up 16-45% of white blood cells. Of those lymphocytes, about half are T cells, a quarter are B cells, and another quarter are natural killer cells.
There are several ways to count T cells and the normal range may vary with the method used.
What abnormal results mean Return to top
Greater-than-normal T-cell levels may indicate: Less-than-normal T-cell levels may indicate:What the risks are Return to top
Risks associated with having blood drawn are slight:Special considerations Return to top
This test can be affected by:
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Page last updated: 28 October 2004 |