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T-cell count

A T-cell count measures the number of T cells in the blood. Your doctor may order this test if you have signs of a weak immune system such as due to having HIV/AIDs .

Alternative Names

Thymus derived lymphocyte count; T-lymphocyte count

How the Test is Performed

A blood sample is needed.

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. Others feel only a prick or stinging sensation. Afterward, there may be some throbbing or a slight bruise. These soon go away.

Why the Test is Performed

T cells are a type of lymphocyte. Lymphocytes are white blood cells. They make up part of the immune system. T cells help the body fight diseases or harmful substances.

Your doctor may order this test if you have signs of a weak immune system (immunodeficiency disorder ). It may also be ordered if you have a disease of the lymph nodes. Lymph nodes are small glands that make white blood cells.The test is also used to monitor how well treatment for these types of diseases is working.

One type of T cell is the CD4 cell, or “helper cell.” Persons with HIV/AIDS have regular T-cell tests to check their CD4 cell counts. The results help the doctor monitor the disease and its treatment.

Normal Results

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.

What Abnormal Results Mean

Higher than normal T-cell levels may be due to:

Lower than normal T-cell levels may be due to:   

The following can affect test results:

  • Chemotherapy medications
  • Corticosteroids
  • Immunosuppressive medications
  • Radiation therapy
  • Stress
  • Surgery

Risks

Risks associated with having blood drawn are slight:

  • Excessive bleeding
  • Fainting or feeling light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)
  • Multiple punctures to locate veins

This test is often performed on people with weakened immune systems. Therefore, the risk for infection may be higher than when blood is drawn from a person with a healthy immune system.

References

Berliner N. Leukocytosis and leukopenia. In: Goldman L, Schafer AI, eds. Goldman’s Cecil Medicine. 24th ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 170.

McPherson RA, Massey HD. Overview of the immune system and immunologic disorders. In: McPherson RA, Pincus MR, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 43.

Updated: 8/4/2013

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, Bethanne Black, and the A.D.A.M. Editorial team.


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