A T-cell count is a blood test that measures the number of T-cells in your body. T-cells are a type of white blood cells, which may also be called lymphocytes. These cells work to fight off diseases. Sometimes your body has too many or too few T-cells. This may be a sign that your immune system is not functioning properly.
A T-cell count may also be called a thymus- derived lymphocyte count, or a T-lymphocyte count.
If you are HIV-positive , this test may be called a CD4 cell count. Some of your T-cells contain a CD4 receptor—this receptor is where the HIV virus 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 are experiencing symptoms of an immunodeficiency disorder, such as HIV, or other conditions, such as cancer or leukemia.
Symptoms of an immunodeficiency disorder include:
- frequent, recurring infections
- severe infections from bacteria or other organisms that do not usually cause severe infections
- trouble recovering from illnesses
- infections that are not responding to treatments
- recurring fungal infections, such as yeast infections
A low T-cell count is more common that a high T-cell count. Low T-cell counts usually indicate problems with the immune system or the lymph nodes. This condition may be caused by:
- viral infections, such as influenza
- immunodeficiency disorders, such as DiGeorge syndrome and Job syndrome
- exposure to radiation
- HIV and AIDS
- cancers that affect the blood or lymph nodes, including Waldenstrom’s macroglobulin, leukemia, and Hodgkin’s disease
- congenital T-cell deficiency (in rare cases)
Less often, you might have a T-cell count that is higher than normal . This can be caused by:
- infectious mononucleosis, which may also be called mono or “the kissing disease”
- acute lymphocytic leukemia, a type of cancer that affects the white blood cells
- multiple myeloma, a type of cancer that affects the plasma in bone marrow
A T-cell count requires only a small sample of your blood, so there is little you need to do to prepare for it.
You should be sure to tell your doctor about all the medications you are 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 he or she will change the dosage before your test.
Medications that may affect your T-cell count include:
- chemotherapy drugs
- radiation therapy
- immunosuppressive drugs or anti- rejections drugs, including glucocorticoids, and antibodies
Your T-cell count can also be affected if you have recently had surgery or gone through a highly stressful experience. You should tell your doctor if any of these situations apply to you.
Remember, a T-cell count requires that your doctor takes only a small sample of your blood. This procedure may also be called a blood draw, or venipuncture. You may have the test in a medical laboratory or in a doctor’s office.
The technician will begin by cleaning an area of skin on your arm or hand with antiseptic to help prevent infection.
An elastic band will be tied around your upper arm so that blood collects in your vein.
Next, a sterile needle will be inserted into your vein and blood will be drawn into a tube. The amount of blood drawn depends on the number of tests that your doctor has ordered, but it should take no longer than a couple of minutes to collect the blood sample needed. The elastic band will be removed while the blood is being drawn.
You may feel some pain while your blood is being drawn —either a pricking or stinging sensation. You can help ease this pain by relaxing your arm. When the technician is finished drawing blood, he or she will remove the needle and apply a bandage to the puncture wound. You should apply pressure to the wound to stop bleeding and prevent bruising.
You will be free to go about your day following the blood draw. Your sample will be sent to a laboratory, where technicians will count the number and type of white blood cells present. According to the U.S. Department of Health and Human Services, your count should be between 500 and 1,000 T-cells per cubic millimetre of blood (HHS).
If your results are above or below this range, your doctor will call you in to discuss any further tests that are necessary for a diagnosis and to plan for possible treatment options.
There are very few risks associated with a T-cell count test. However, this test is often done on individuals who have a compromised immune system and 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 as a result of having trouble when finding a vein
- excessive bleeding
- feeling light-headed or fainting
- hematoma, which is a collection of blood under the skin
- infection at the puncture site