CD4+ Count

A CD4+ count is a blood test to determine how well the immune system is working in people who have been diagnosed with human immunodeficiency virus (HIV). CD4+ cells are a type of white blood cell. White blood cells are important in fighting infections. CD4+ cells are also called T-lymphocytes, T-cells, or T-helper cells.

HIV infects CD4+ cells. The number of CD4+ cells helps determine whether other infections (opportunistic infections) may occur. The pattern of CD4+ counts over time is more important than any single CD4+ value because the values can change from day to day. The CD4+ pattern over time shows the effect of the virus on the immune system. In people infected with HIV who are not getting treated, CD4+ counts generally decrease as HIV progresses. A low CD4+ count usually indicates a weakened immune system and a higher chance of getting opportunistic infections.
Why It Is Done

CD4+ counts are done to:

    Monitor how the HIV infection is affecting your immune system.
    Help diagnose acquired immune deficiency syndrome (AIDS). HIV infection can progress to AIDS, which cannot be cured.
    Decide when to start antiretroviral therapy, which slows the rate that HIV multiplies in the body. See the Results section for more information.
    Evaluate your risk for other infections (opportunistic infections).
    Decide when to start treatment to prevent opportunistic infections, such as medicines to prevent Pneumocystispneumonia.

A CD4+ cell count taken at the time you are diagnosed serves as the baseline against which future CD4+ cell counts will be compared. Your CD4+ cell count is monitored every 3 to 6 months, depending on your health status, previous CD4+ cell counts, and whether you are taking highly active antiretroviral therapy (HAART) medicines.
How To Prepare

Before you have this test, you may have the opportunity to meet with a counselor so that you understand what the test results could mean about your HIV infection.
How It Is Done

The health professional drawing blood will:

    Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
    Clean the needle site with alcohol.
    Put the needle into the vein. More than one needle stick may be needed.
    Attach a tube to the needle to fill it with blood.
    Remove the band from your arm when enough blood is collected.
    Apply a gauze pad or cotton ball over the needle site as the needle is removed.
    Apply pressure to the site and then a bandage.

How It Feels

You may feel nothing at all from the needle puncture, or you may feel a brief sting or pinch as the needle goes through the skin. Some people feel a stinging pain while the needle is in the vein. But many people do not feel any pain (or have only minor discomfort) after the needle is positioned in the vein. The amount of pain you feel depends on the skill of the health professional drawing the blood, the condition of your veins, and your sensitivity to pain.

Risks

There is very little risk of complications from having blood drawn from a vein.

    You may develop a small bruise at the puncture site. You can reduce the risk of bruising by keeping pressure on the site for several minutes after the needle is withdrawn.
    In rare cases, the vein may become inflamed after the blood sample is taken. This condition is called phlebitis and is usually treated with a warm compress applied several times daily.
    Continued bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can also make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your health professional before your blood is drawn.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

    The time of day when the CD4+ is measured. CD4+ counts may be lower in the morning.
    Illnesses, such as pneumonia, herpes simplex infection, or influenza.
    Refrigeration of the blood sample.
    Medicines, such as corticosteroids and chemotherapy medicines.

What To Think About

    The pattern of CD4+ counts over time is more important than any single CD4+ value. CD4+ counts typically decrease as HIV progresses.
    Your doctor may look at your CD4+ count and your viral load to help decide when to start antiretroviral treatment. The CD4+ cell count is often done with viral load testing to measure the effectiveness of antiretroviral therapy. The viral load test measures the actual amount of HIV in the blood, which is a good indicator of how well medicines are controlling the HIV infection. In some cases, viral load testing may be done instead of the CD4+ count. For more information, see the topic Viral Load Measurement.
    Highly active antiretroviral therapy (HAART) may help your immune system if you develop certain illnesses but still have a good CD4+ count.
    Because total CD4+ count can vary throughout the day, many doctors also monitor the number of CD4+ cells in the total number of lymphocytes. This measurement is called the CD4+ percentage.
    Another measurement that may be used is the CD4 count (T helper cells) in comparison with the CD8 count (T suppressor cells). This is called the CD4/CD8 ratio. All of these measurements can help determine the effectiveness of HIV treatment.
    Testing for HIV infection is a different test. For more information, see the topic Human Immunodeficiency Virus (HIV) Test.