What are Lymphocytes?
A CD4 count is a test that measures the number of CD4 cells in your blood. CD4 cells, also known as T cells, are white blood cells that fight infection and play an important role in your immune system. A CD4 count is used to check the health of the immune system in people infected with HIV (human immunodeficiency virus).
HIV attacks and destroys CD4 cells. If too many CD4 cells are lost, your immune system will have trouble fighting off infections. A CD4 count can help your health care provider find out if you are at risk for serious complications from HIV. The test can also check to see how well HIV medicines are working.
Other names: CD4 lymphocyte count, CD4+ count, T4 count, T-helper cell count, CD4 percent
What is it used for?
A CD4 count may be used to:
- See how HIV is affecting your immune system. This can help your health care provider find out if you are at higher risk for complications from the disease.
- Decide whether to start or change your HIV medicine
- Diagnose AIDS (acquired immunodeficiency syndrome)
- The names HIV and AIDS are both used to describe the same disease.But most people with HIV don't have AIDS. AIDS is diagnosed when your CD4 count is extremely low.
- AIDS is the most severe form of HIV infection. It badly damages the immune system and can lead to opportunistic infections. These are serious, often life-threatening, conditions that take advantage of very weak immune systems.
You may also need a CD4 count if you've had an organ transplant. Organ transplant patients take special medicines to make sure the immune system won't attack the new organ. For these patients, a low CD4 count is good, and means the medicine is working.
Why do I need a CD4 count?
Your health care provider may order a CD4 count when you are first diagnosed with HIV. You will probably be tested again every few months to see if your counts have changed since your first test. If you are being treated for HIV, your health care provider may order regular CD4 counts to see how well your medicines are working.
Your provider may include other tests with your CD4 count, including:
- A CD4-CD8 ratio. CD8 cells are another type of white blood cell in the immune system. CD8 cells kill cancer cells and other invaders. This test compares the numbers of the two cells to get a better idea of immune system function.
- HIV viral load, a test that measures the amount of HIV in your blood.
What happens during a CD4 count?
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
Will I need to do anything to prepare for the test?
You don't need any special preparations for a CD4 count.
Are there any risks to the test?
There is very little risk to having a blood test. You may have slight pain or bruise at the spot where the needle was put in, but most symptoms go away quickly.
