What is a CD4 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. 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.

Other names: CD4 lymphocyte count CD4+ count, T4 count, T-helper cell count, CD4 percent

What is it used for?

If you have HIV, a CD4 count may be used to:

• See how HIV is affecting your immune system. CD4 counts can help monitor your risk for developing opportunistic infections or certain cancers. If your risk increases, your provider may give you treatment to help prevent infections.
• Help check how well HIV treatment is working. A CD4 count is used with a test called an HIV viral load test to see if HIV medicines are working. A viral load tests measures how much HIV is in your blood.
• Diagnose AIDS. Without treatment, HIV can lead to a very low CD4 count, which means you have AIDS.

A CD4 count may also be used to:

• Monitor treatment after an organ transplant. If you've had an organ transplantation, you'll need to take medicine to prevent your immune system from attacking the new organ. These medicines are called "anti-rejection" drugs or immunosuppressants. You may also take these medicines to treat certain autoimmune diseases. A low CD4 count means the medicine is working.
• Help diagnose different types of lymphoma. A CD4 count may be used with other tests to find out which type of immune cells are causing lymphoma. The test results help choose the right treatment.
• Help diagnose DiGeorge syndrome. This is an uncommon inherited disorder that often causes immune problems and other health conditions that start at birth.

Why do I need a CD4 count?

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.

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 bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

CD4 results are usually given as a number of cells per cubic millimeter of blood. But labs may have different ways of describing "normal" CD4 counts. What's normal for you depends on your age, other health conditions, and the medicines you may take. That's why it's important to talk with your provider about what your test results mean.

CD4 counts may change even when your health has not changed. So, your provider will usually look at a few test results over time to see if there's a trend in your CD4 counts.

In general, ranges for CD4 counts are:

• Normal CD4 count for healthy adults and teens: 500 to 1,200 cells per cubic millimeter
• Low CD4 count: Below 500 cells per cubic millimeter
  • If you have HIV, a low CD4 count means that HIV has weakened your immune system. A CD4 count of 200 or fewer cells per cubic millimeter means that you have AIDS. With AIDS you have a high risk of developing life-threatening infections or cancers.
  • If you don't have HIV, a low CD4 count may be caused by an infection. Cancer chemotherapy and medicines that weaken your immune system may also cause low CD4 counts. In certain cases, the cause of a low CD4 count is unknown, but this is uncommon.
• High CD4 Count: Counts above the normal range may be sign of an infection or a blood cancer.

While there is no cure for HIV, there are different medicines that you can take to control the virus and protect your immune system. In fact, CD4 counts usually increase with these medicines, which helps keep you healthy. If you are living with HIV, it's important to take your medicine as prescribed and get regular blood tests, including CD4 counts.

Learn more about laboratory tests, reference ranges, and understanding results.