Viral load (ARN VIH) measures the amount of HIV in the blood, is a measure of the activity of the virus and that is so well functioning treatment; in conjunction with CD4 count helps to make decisions about the beginning of the treatment. Viral load can vary from very low (less than 50 75 copies genetic per milliliter of blood) to very high (millions of copies). The highest point occurs during the acute retroviral syndrome or people in advanced stages of the disease. When the treatment is effective, the viral load is very low, almost undetectable (less than 50), be undetectable does not mean that there are no viruses, simply means that the viral load is very low as to which appears on standard blood tests. The viral load should be measured regularly (every 3 or 4 months) regardless of whether the patient is attending a treatment or not, but it is important that once started the TAR viral load tests be made often since this will show if drugs are still effective or not. The viral load should decrease 10 times during the first month of treatment (for example, from 100,000 to 10,000) and should be undetectable within 3 or 4 months, depending on that so high was when the treatment was started.

If the viral load is detectable when it is not a cause for alarm, it may be something passed, as a single viral load that is detectable at low levels (from 50 to 1000). Outbreaks of this type appear as a result of a variation of the test, since this is not 100% accurate, by what they generally do not lead to anything. Obviously, only knows if it is passed, once repeated the test, which is important to do so, since a detectable viral load can be indicator that the treatment is not effective.