HIV is a disease caused by the human immunodeficiency virus. This virus works by attacking special immune system cells known as CD4 cells or T-cells. When a person is infected with HIV, the virus invades CD4 cells and uses them to manufacture more of the virus so the infection will spread.
If you have HIV, your doctor will want to track your viral load which shows how much HIV virus is active in your body. He will also want to monitor your CD4 cell count.
CD4 and CD8 are two different kinds of white blood cells which are part of your immune system. These cells circulate throughout your body to fight infections. CD4 cells are targeted by the HIV virus. When a CD4 cell is invaded by HIV, the cell dies and is no longer able to do its job in the immune system.
Because HIV is not a living virus, it cannot reproduce itself. Instead, when it invades a CD4 cell it takes over the genetic material in the cell and uses that material to create new copies of its genetic code, which is called RNA. The viral RNA is then released back into the bloodstream to target new CD4 cells to repeat the replication process.
As the amount of HIV virus in your body goes up (viral load) the number of health CD4 cells will go down. Doctors order tests to monitor the CD4 cell count to track how healthy your immune system is. Your doctor may also check to see how the number of CD4 cells compares to the number of CD8 cells in your blood, as another way to tell if you are more prone to serious infections.
There are three different ways doctors look at the CD4 count.
• Absolute level – this is the number of CD4 cells found in a specific amount of blood.
• Ratio to CD8 – this is the comparison between CD4 and CD8 cells
• Percent total lymphocytes – A lymphocyte is an immune system cell. CD4 and CD8 are just two of the many types of lymphocytes at working to keep you healthy.
Knowing your CD4 count allows your doctor to keep track of how strong your immune system is. The time of day when the test is done and other factors can influence your CD4 count, so your doctor will track your count over time to watch for trends.