T (Thymus Derived) Lymphocyte 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; T cell 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. Afterward, there may be some throbbing or a slight bruise. This soon goes 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, such as bacteria or viruses.

Your health care provider 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." People with HIV/AIDS have regular T-cell tests to check their CD4 cell counts. The results help the provider monitor the disease and its treatment.

Normal Results

Normal results vary depending on the type of T-cell tested.

In adults, a normal CD4 cell count ranges from 500 to 1,200 cells/mm3.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.

What Abnormal Results Mean

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

  • Cancer, such as acute lymphocytic leukemiaor multiple myeloma
  • Infections, such as hepatitis or mononucleosis

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

  • Acute viral infections
  • Aging
  • Cancer
  • Immune system diseases, such as HIV/AIDS
  • Radiation therapy
  • Steroid treatment


Risks associated with having blood drawn are slight:

  • Excessive bleeding
  • Fainting or feeling lightheaded
  • 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 a weakened immune system. Therefore, the risk for infection may be higher than when blood is drawn from a person with a healthy immune system.


Berliner N. Leukocytosis and leukopenia. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 167.

Holland SM, Gallin JI. Evaluation of the patient with suspected immunodeficiency. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 12.

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.

Review Date: 8/29/2015

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