CD3 count
Key points
- This is a blood test that measures the number of T-lymphocytes (a type of white blood cell).
- Blood is drawn from a vein on the inside of the elbow or the back of the hand.
- For infants and children: The preparation you can provide for this test depends on your child's age and experience.
- A T-cell count of may be helpful in the diagnosis of immunodeficiency diseases and lymphocytic diseases.
Alternative names
T cell counts; CD4 count; T (thymus derived) lymphocyte count; T-lymphocyte count
Definition
This is a blood test that measures the number of T-lymphocytes (a type of white blood cell).
How the test is performed
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
No special preparation is necessary.
For infants and children:
The preparation you can provide for this test depends on your child's age and experience. For specific information regarding how you can prepare your child, see the following topics:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- Schoolage test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
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.
Written and revised by
Andrey Nailor, M.D.
Our doctors write and review articles for accuracy and keep them up to date.
health.am provides general information, not medical advice. Always consult a qualified health professional about your own health.