The B and T cell screen is a blood test that measures the level of lymphocytes in your blood. Lymphocytes are a type of white blood cell (WBC) that helps your body’s immune system identify and fight off organisms or substances that cause diseases.

The two predominant types of lymphocytes that are created in your bone marrow are B cells and T cells. An antigen is a foreign substance, such as a chemical, virus, or bacteria. When an antigen enters your body, B cells produce antibodies that attach to the substance. However, these antibodies aren’t strong enough to kill the antigen. T cells direct your body’s response to the presence of a foreign molecule and kill infected cells.

There are two parts to your body’s immune system. The first is innate protection, which consists of proteins and cells that are always in your body. This innate protection provides a general defense that’s always ready to protect your body from foreign invaders.

The second part of your immune system is adaptive protection, which is made up of the B and T cells. The B and T cells are produced to target invaders that make it past your innate immune defenses. When antigens bypass the first system of protection, your body’s best defense is its B and T cells. When your immune system is weakened or damaged, your B and T cells are unable to function correctly.

Sometimes, the immune system attacks and destroys healthy tissue because it can’t tell the difference between antigens and healthy cells. When this happens, it’s known as an autoimmune disorder.

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

  • a low WBC count
  • thyroid problems
  • liver failure
  • swollen lymph nodes
  • recurrent or unusual infections

Before any medical test is performed, tell your doctor about any of the following that you’re taking:

  • prescription medications
  • non-prescription medications
  • dietary supplements
  • vitamins

Make sure to tell your doctor if you have an autoimmune disease, have recently had surgery, or if you’re currently taking medications to suppress your immune system. These factors may affect your results.

The B and T cell screen is a blood test. The following steps are involved:

  1. A healthcare provider will tie an elastic band called a tourniquet above the site where the blood will be taken, which is usually on the inside of your elbow.
  2. They’ll clean the area and sterilize it with antiseptic before inserting a small needle directly into your vein. Most people feel a sharp pain at the initial needle poke that quickly fades as their blood is drawn.
  3. Within a few minutes, the healthcare provider will remove the needle and apply pressure to the site with a cotton ball.
  4. They’ll place a bandage on the site, and you’ll be free to leave.

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

Your immune system is a very complex part of your 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 (TB)
  • infectious mononucleosis, or mono, which is a viral infection that affects the lymph glands
  • multiple myeloma, which is a cancer that originates in the plasma and bone marrow
  • DiGeorge syndrome, which is a chromosomal disorder that’s associated with heart defects and thyroid issues

Decreased levels of T or B cells are often associated with:

  • congenital, or inherited, immunodeficiency disorders
  • certain cancers in your blood
  • certain cancers in your lymphatic cells
  • acquired immune disorders, such as HIV or AIDS

Additional tests may be necessary to rule out certain disorders and make a diagnosis. These may include:

  • an IgE level measurement to determine the amount of a certain type of antibody in your blood
  • a lymph node biopsy
  • a peripheral blood smear
  • a bone marrow biopsy

Your doctor will evaluate your results and discuss the best form of treatment with you.