Monday, 24 February 2014

HIV, AIDS, and the CD4 Count

CD4 cells are a type of white blood cell that fights infection. Another name for them is T-helper cells. CD4 cells are made in the spleen, lymph nodes, and thymus gland, which are part of the lymph or infection-fighting system. CD4 cells move throughout your body, helping to identify and destroy germs such as bacteria and viruses.

The CD4 count measures the number of CD4 cells in a sample of your blood drawn by a needle from a vein in your arm. Along with other tests, the CD4 count helps tell how strong your immune system is, indicates the stage of your HIV disease, guides treatment, and predicts how your disease may progress. Keeping your CD4 count high can reduce complications of HIV disease and extend your life.

How HIV Affects CD4 Cells

HIV targets CD4 cells by:

Binding to the surface of CD4 cells
Entering CD4 cells and becoming a part of them. As CD4 cells multiply to fight infection, they also make more copies of HIV
Continuing to replicate, leading to a gradual decline of CD4 cells
HIV can destroy entire "families" of CD4 cells. Then the diseases these "families" were designed to fight can easily take over. That's when opportunistic infections are likely to develop.

When to Have a CD4 Count Test

Your doctor will recommend a CD4 count test:

When you're first diagnosed with HIV. This is called a baseline measurement. It allows you to compare against future measurements.
About two to eight weeks after starting or changing treatment.
Every three to six months.

What the CD4 Count Test Results Mean

CD4 counts are reported as the number of cells in a cubic millimeter of blood. A normal CD4 count is from 500 to 1,500 cells per cubic millimeter of blood. It is more important to pay attention to the pattern of results than to any one test result.

In general, HIV disease is progressing if the CD4 count is going down. This means the immune system is getting weaker and you are more likely to get sick. In some people, CD4 counts can drop dramatically, even going down to zero.

The test does not always correspond with how well you are feeling. For example, some people can have high CD4 counts and do poorly. Others can have low CD4 counts and have few complications.

If your CD4 count goes down over several months, your doctor may recommend:

Beginning or changing antiretroviral therapy.
Starting preventive treatment for opportunistic infections.
Public health guidelines recommend starting on preventive antiretroviral therapy if CD4 counts are under 200, whether or not you have symptoms. This is a later stage of HIV infection called AIDS (acquired immunodeficiency syndrome). Some doctors start therapy earlier, when the CD4 count reaches 350 to 500 or if you have a newly acquired infection. If therapy is effective, your CD4 count should go up or become stable.

Most doctors recommend starting medication for opportunistic infections at these levels:

Less than 200: pneumocystis pneumonia (PCP).
Less than 75: mycobacterium avium complex (MAC).

Factors That Can Affect Your CD4 Count

You should know that other factors can influence how high or low your CD4 count is.

CD4 counts tend to be lower in the morning and higher in the evening.
Acute illnesses such as pneumonia, influenza, or herpes simplex virus infection can cause CD4 counts to go down for a while.
If you have a vaccination or when your body starts to fight an infection, your CD4 counts can go up or down.
Cancer chemotherapy can cause CD4 counts to go way down.
Fatigue and stress can also affect test results.
For these reasons:

Try to use the same lab each time.
Have your tests done at the same time of day each time.
Wait for at least a couple of weeks after an infection or vaccination before getting a CD count test.