CD4 Lymphocyte Count

A CD4 count is a blood test that measures the number of CD4 cells in a sample of your blood. CD4 cells are a type of white blood cell that circulates throughout the body in the blood. They're also called CD4 T lymphocytes or 'helper T cells.' That's because they help fight infection by triggering your immune system to destroy viruses, bacteria, and other germs that may make you sick.

A CD4 count is mostly used to check the health of your immune system if you are infected with HIV (human immunodeficiency virus). HIV attacks and destroys CD4 cells. Without treatment, HIV may destroy so many CD4 cells that your immune system will have trouble fighting off infections.

HIV is the virus that causes AIDS (acquired immunodeficiency syndrome). AIDS is the most serious stage of an HIV infection. If you have AIDS, your CD4 count is so low that you may develop serious infections from viruses, bacteria, or fungi that usually don't cause problems in healthy people.

These are called 'opportunistic infections,' and they can become life-threatening. AIDS increases your risk of developing certain cancers, too. Most people with HIV don't have AIDS.

And if they take their HIV medicine as prescribed, they may never develop AIDS. If you have HIV, a CD4 count can help your health care provider check your risk for serious infections. A CD4 count may also be used to help diagnose and monitor certain other conditions that affect your immune system.

Why this test is done

Your 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 taking medicine for HIV, your provider may order regular CD4 counts with an HIV viral load test to see how well your medicines are working.

How to prepare

You don't need any special preparations for a CD4 count.

Sample type

Blood

Other names for this test

CD4 lymphocyte count CD4+ count, T4 count, T-helper cell count, CD4 percent