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

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.

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

• Chemotherapy
• Surgery
• Steroid therapy
• Stress
• X-rays

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.

Your doctor may order this test if you have signs of an immunodeficiency diseases. It may also be used to distinguish between cancerous and noncancerous disease. The test may also be used to determine how well treatment for certain conditions is working.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

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:

• Infectious mononucleosis
• Multiple myeloma
• Acute lymphoblastic leukemia

An increased B cell count may be due to:

• Chronic lymphocytic leukemia
• Multiple myeloma
• Waldenstrom's macroglobulinemia
• DiGeorge syndrome

A decreased T cell count may be due to:

• Congenital T-cell deficiency disease
  • Nezelof syndrome
  • DiGeorge syndrome
  • Wiskott-Aldrich syndrome
• B cell proliferative disorders
  • Acquired immunodeficiency syndrome
  • Chronic lymphocytic leukemia
  • Waldenstrom's macroglobulinemia

A decreased B cell count may be due to:

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

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)