HIV viral load tests measure the amount of HIV in the blood. Lower levels are better than higher levels. The main goal of HIV drugs is to reduce the HIV viral load to an "undetectable" level, meaning that the HIV RNA is below the level that the test is able to count.

The lower limit of HIV RNA detection depends on the test used--some go down to 50 copies/ml, while other go as low as 20. High viral loads are linked to faster disease progression. Reducing the viral load to "undetectable" levels slows or stops disease progression and prevents HIV transmission to sex partners. Treatment for HIV suppresses the virus but does not eliminate it. Even if HIV levels are not detectable in the bloodstream, HIV is still in the body and will rebound to detectable if the HIV medicines are stopped.

CD4 counts and HIV viral load tests are usually done when you first see a medical provider and about every 3 months afterwards. Results tell whether the HIV medications are working well; and for people who have chosen to delay taking medicines, they can help you and your provider monitor your health and decide how urgent it is for you to start taking HIV drugs or medicines to prevent infections (more on this in Treatment Decisions).