B and T Cell Screen

Written by Lydia Krause | Published on August 15, 2012
Medically Reviewed by Peter Rudd, MD

What Is a B and T Cell Screen?

The B and T cell screen measures the level of lymphocytes within the body’s blood. Lymphocytes are a type of white blood cell that helps your body’s immune system identify and fight disease-causing organisms or substances.

There are two types of lymphocytes, which are created in the bone marrow: B cells and T cells. When an antigen (foreign substance like a chemical, virus, or bacteria) enters your body, B cells produce antibodies that attach to the substance. However, these antibodies are not strong enough to kill the antigen. T cells direct the body’s response to the presence of a foreign molecule and kill infected cells.

There are two parts to the body’s immune system. The first is the innate protection and the second is adaptive protection. When pathogens bypass the first system of protection, the body’s best defense is its B and T cells. When the immune system is weakened or damaged, the B and T cells are unable to function correctly.

Sometimes the immune system attacks and destroys healthy body tissue because it cannot tell the difference between antigens and healthy cells. When this happens, it is known as an autoimmune disorder.

Why Is My Doctor Ordering This Test?

The B and T cell screen test may be performed if you have symptoms of diseases that weaken the immune system, or diseases of the blood and bone marrow. Some common symptoms include:

  • low complete blood count (CBC) test result
  • thyroid problems
  • liver failure
  • swollen lymph nodes
  • recurrent or exotic infections

What Should My Doctor Know Before I Take the Test?

Before any medical test is performed, it is essential you tell your doctor about any prescription or non-prescription medications, dietary supplements, and vitamins that you’re currently taking. Make sure to tell your doctor if you suffer from an autoimmune disease, recently had surgery, or are currently taking medication to suppress your immune system, as these factors may affect your results.

What Happens During the Test?

The B and T cell screen is a blood test. A nurse will tie an elastic band (tourniquet) above the site where the blood will be taken, usually on the inside of the elbow. The area will be cleaned and sterilized with antiseptic before a small needle is inserted directly into the vein.

Most people feel a sharp pain at the initial needle poke, which quickly fades as the blood is drawn. Within a few minutes, the needle will be removed and you will be asked to apply pressure to the site with a cotton ball. A bandage will be placed on the site and you will be free to leave.

Blood tests are typically painless and carry low risk. However, you may experience slight bruising or temporary discomfort after blood is drawn. Some people experience minor dizziness after having blood drawn. Let your doctor or nurse know if you feel dizzy, faint, or nauseous.

What Does an Abnormal Result Mean?

The immune system is a very complex part of the body and abnormal cell counts can indicate a variety of disorders.

Common diseases and disorders associated with increased levels of T or B cells include:

  • certain types of leukemia
  • tuberculosis
  • mononucleosis (a viral infection that affects the lymph glands)
  • multiple myeloma (a cancer that originates in the plasma and bone marrow)
  • DiGeorge syndrome (a chromosomal disorder that is associated with heart defects and thyroid issues)

Decreased levels of T or B cells are often associated with congenital (inherited) immunodeficiency disorders, certain cancers in the blood or lymphatic cells, or acquired immune disorders, such as HIV or AIDS.

What Happens Next?

Additional tests may be necessary to rule out certain disorders and make a diagnosis. Your doctor will evaluate your results and discuss the best form of treatment with you.

Medical tests corresponding with the B and T cell screen test may include:

  • IgE level measurement (a test that measures the amount of a certain type of antibody in the blood)
  • lymph node biopsy
  • peripheral blood smear
  • bone marrow biopsy
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