CD4 and CD8 cells are white blood cells that play important roles in your body’s immune response. Tests that count your CD4 and CD8 cells provide a picture of your immune system health. Along with your viral load, your CD4 cell count can help your doctor tell whether your HIV disease is progressing or not, and how well your HIV drugs are working.
- CD4 cells (sometimes called T-helper cells)
These white blood cells help coordinate the various activities of your immune system. HIV targets CD4 cells more than any other kind of cell in your body. A normal CD4 cell count is about 600-1,500 cells. CD4 cell counts are often slightly higher in HIV+ women compared to HIV+ men (viral load in HIV+ women also tends to be slightly higher, relative to men, at the same stage of disease). CD4 cell counts usually fall as HIV disease progresses.
- CD8 cells (T-suppressor or killer T cells)
There are two main types of CD8 cells. T-suppressor cells inhibit or suppress immune responses. Killer T cells attack (“kill”) cancerous cells and cells infected with viruses. A normal CD8 cell count is about 300–1,000 cells. CD8 cell counts usually rise over time in HIV+ people, but why and how these increases relate to the health of your immune system is not well understood.
Without HIV medication, the virus infects more and more cells. This causes the CD4 count to decrease, usually by about 30 to 100 cells per year, in most HIV+ people. As the CD4 count goes down, an HIV+ person becomes more likely to develop opportunistic infections and cancers.
- Above 500: People with CD4 counts above 500 cells usually have fairly normal immune function and are at low risk for OIs
- Below 350: Current U.S. government guidelines recommend that you should consider HIV treatment when your CD4 count falls below 350 cells
- Below 200: A person with a CD4 cell count below 200 cells is diagnosed as having AIDS. The guidelines recommend starting treatment at this point, if you have not already done so
People with low CD4 counts are prone to developing OIs such as Pneumocystis carinii pneumonia (PCP), Mycobacterium avium complex (MAC), and cytomegalovirus (CMV). As CD4 cells drop below 200, your doctor will recommend medications to prevent these infections.
Many people have dramatic CD4 cell increases when they start effective HIV treatment. If the drugs succeed in slowing or stopping HIV replication, fewer new CD4 cells will be infected and the CD4 count can recover—the “proof” of which you see by the increasing numbers. But the CD4 count can also fall again if you stop taking your drugs correctly, or if your HIV becomes resistant to the drugs. So, your CD4 count is a very valuable tool for monitoring your HIV disease progression and how well your HIV medicines are working.
The U.S. government treatment guidelines now recommend that people consider starting HIV treatment when their CD4 cell counts fall below 350 cells. The recommended level for starting treatment used to be 500 cells. This change was made because researchers found that starting treatment with more than 350 but less than 500 CD4 cells did not add much benefit.
CD4 and CD8 cell tests are simple blood tests ordered by your doctor. When you are first diagnosed as HIV+ or when you first start treatment, you should get “baseline” CD4 and CD8 cell tests. Baseline tests give a current picture of your immune system, when you first enter a doctor’s care. Later tests can be compared against these first results to see how things are changing over time and with treatment.
You should get your CD4 cell count checked about every three to six months--or as often as your doctor recommends. You may need more frequent CD4 cell tests if your count is low or falling, or if you are starting or changing treatment.
Many factors can affect your CD4 cell count, including the time of day, stress, your menstrual cycle, and infections such as the flu. If you get a result or number back that surprises you or your doctor, your doctor will probably want you to get a second test. That second test would confirm any unexpected results or prove that those results were random, sort of a fluke (that is, not significant). Don’t worry too much about a single abnormal test result; trends over time are usually more important.
In addition to CD4 and CD8 cell counts, your doctor may also want to know your CD4 or CD8 percentage. Percentages are usually more stable than counts over time. A normal CD4 cell percentage is about 30-60 percent, and a normal CD8 cell percentage is about 20-50 percent. Sometimes doctors also look at the CD4/CD8 ratio. Healthy HIV- people usually have at least 1-2 CD4 cells for every CD8 cell. But HIV+ people may have many more CD8 cells than CD4 cells.
Because HIV attacks CD4 cells, CD4 counts usually drop as HIV disease progresses. Taking effective combinations of HIV drugs may stop CD4 cell count decreases and HIV disease progression.
Your CD4 cell count is an important indicator of the health of your immune system. Tracking trends in your CD4 cell count can help you make decisions about starting and switching treatment. Getting regular CD4 cell tests—along with viral load tests and other blood tests to monitor treatment side effects—is an important way to take charge of your health.
Highleyman, L. (2003). Monitoring tests for people with HIV. Bulletin of Experimental Treatments for AIDS: Retrieved July 2003 from http://www.sfaf.org/treatment/beta/b53/b53_monitoring.html.
Hogg, R. et. al. (2001). Rates of disease progression based on CD4 cell count and viral load after initiating drug therapy. Journal of the American Medical Association, 286(20). 2568-2577.
National Institute of Allergy and Infectious Diseases. (1999). How does the immune system work?