A T cell count is a blood test that measures the number of T cells in your body. A T cell is a type of white blood cell. White blood cells are also called lymphocytes. These cells fight off diseases. The two categories of lymphocytes are T cells and B cells. The T cells respond to viral infections, while the B cells fight bacterial infections. Your body sometimes has too many or too few T cells. This may be a sign that your immune system isn’t functioning properly.
A T cell count may also be known as a thymus-derived lymphocyte count, or a T lymphocyte count.
If you’re being treated for HIV, this test may be known as a CD4 cell count. Some T cells contain a CD4 receptor. This receptor is where HIV attaches to the T cell. When the number of CD4 T cells drops below a certain point, it may be time for you to begin treatment for HIV and AIDS.
Your doctor may order a T cell count if you’re having symptoms of an immunodeficiency disorder, such as HIV, or other conditions, such as cancer or leukemia.
The symptoms of an immunodeficiency disorder include:
- frequently recurring infections
- severe infections from bacteria or other organisms that don’t usually cause severe infections
- trouble recovering from illnesses
- infections that don’t respond to treatments
- recurring fungal infections, such as yeast infections
- recurring parasitic infections
A low T cell count is more common than a high T cell count. Low T cell counts usually indicate problems with your immune system or lymph nodes. Low T cell counts may be due to:
- viral infections, such as influenza
- immunodeficiency disorders
- exposure to radiation
- HIV and AIDS
- cancers that affect the blood or lymph nodes, such as Waldenstrom’s macroglobulinemia, leukemia, and Hodgkin’s disease
- congenital T cell deficiency in rare cases
Less often, you might have a T cell count that’s higher than normal. A high T cell count can be due to:
- infectious mononucleosis, which is also known as mono or the kissing disease
- acute lymphocytic leukemia, which is a type of cancer that affects the white blood cells
- multiple myeloma, which is a type of cancer that affects the plasma in bone marrow
A T cell count requires only a small sample of your blood. There’s little you need to do to prepare for it.
Be sure to tell your doctor about all the medications you’re taking, including any over-the-counter and prescription medications or herbal supplements, before your test. Certain medications can impact your T cell count, which will alter the results of your test. Your doctor may ask you to stop taking your medications for a little while, or they may change the dosage before your test.
Medications that may affect your T cell count include:
- chemotherapy drugs
- radiation therapy
- immunosuppressive drugs or anti-rejection drugs
Recent surgery or highly stressful experiences can also affect your T cell count. You should tell your doctor if any of these situations apply to you.
Remember, your doctor only needs a small sample of your blood to get a T cell count. This procedure is also known as a blood draw or venipuncture. You may have the test in a medical laboratory or a doctor’s office.
- A healthcare provider will begin by cleaning an area of skin on your arm or hand with antiseptic to help prevent infection.
- They’ll tie an elastic band around your upper arm so that blood collects in your vein.
- Next, they’ll insert a sterile needle into your vein and draw blood into a tube. The amount of blood drawn depends on the number of tests that your doctor ordered. It should take no longer than a couple of minutes to collect the blood sample needed.
- You may feel some pain while having your blood drawn. This usually feels like a pricking or stinging sensation. You can help ease this pain by relaxing your arm. When the technician finishes drawing blood, they’ll remove the elastic band and the needle and apply a bandage to the puncture wound. You should apply pressure to the wound to stop bleeding and prevent bruising.
You’ll be free to go about your day following the blood draw. Your sample will go to a laboratory, where technicians will count the number and type of white blood cells present.
There are very few risks associated with a T cell count. However, people with compromised immune systems often have this test. They may be at greater risk for developing an infection than the rest of the population.
Other possible risks of a T cell test include:
- multiple puncture wounds if the technician has trouble finding a vein
- excessive bleeding
- lightheadedness or fainting
- hematoma, which is a collection of blood under the skin
- an infection at the puncture site
According to the U.S. Department of Health and Human Services, your T cell count should be between 500 and 1,200 T cells per cubic millimeter of blood.
Your doctor will discuss any further tests you need for a diagnosis. They’ll also provide you with treatment options if your results are above or below this range.