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B and T cell screen

Definition

A B and T cell screen is a laboratory test to determine the amount of T and B cells (lymphocytes) in the blood.

Alternative Names

Direct immunofluorescence; E-rosetting; T and B lymphocyte assays; B and T lymphocyte assays

How the Test is Performed

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.

Blood could also be obtained by capillary sample (fingerstick, or heelstick in infants).

After the blood is drawn it goes through a two-step process. First, the lymphocytes are separated from other blood parts. Once the cells are separated, identifiers are added to distinguish between T and B cells. The E-rosetting test identifies T cells and direct immunofluorescence is used to identify B cells.

How to Prepare for the Test

Tell your health care provider if you have had any of the following, which might affect your T and B cell count:

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.

Why the Test is Performed

Your doctor may order this test if you have signs of certain diseases that weaken the immune system. It may also be used to distinguish between cancerous and noncancerous disease, especially cancers that involve the blood and bone marrow.

The test may also be used to determine how well treatment for certain conditions is working.

Normal Results

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

Abnormal T and B cell counts suggest possible diseases. Further testing is needed to confirm a diagnosis.

An increased T cell count may be due to:

An increased B cell count may be due to:

A decreased T cell count may be due to:

  • Congenital T-cell deficiency disease
    • Nezelof syndrome
    • DiGeorge syndrome
    • Wiskott-Aldrich syndrome
  • Acquired T-cell deficiency states
  • B cell proliferative disorders

A decreased B cell count may be due to:

  • Acute lymphoblastic leukemia
  • Congenital immunoglobulin deficiency disorders
  • Acquired immunoglobulin deficiency disorders

Risks

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

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

References

Bagby GC. Leukopenia and leukocytosis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 173.

Review Date: 8/28/2009
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School, Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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