Test Overview

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.
• Evaluate your risk for other infections (opportunistic infections).
• Decide when to start treatment to prevent opportunistic infections, such as medicines to prevent Pneumocystis pneumonia.

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 antiretroviral therapy medicines.

How To Prepare

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

How It Is Done

A health professional uses a needle to take a blood sample, usually from the arm.

How It Feels

When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

Risks

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.

Results

CD4+ cell count results are generally available in 1 to 3 days, depending on the lab.

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

In people with human immunodeficiency virus (HIV), as the CD4+ count drops, it becomes more likely that acquired immunodeficiency syndrome (AIDS) will develop.