Testing during primary infection

Viral loads tests (HIV RNA) may be used to detect the presence of HIV in the body prior to the development of antibodies. The standard means of identifying HIV-positive people is through the use of antibody tests. The appearance of antibodies in the blood is often accompanied by a seroconversion illness. Seroconversion is often preceded by a burst in viral replication, and high viral load is common among people recently exposed to HIV.

If HIV infection is suspected (for example, someone knows or suspects they were exposed through sexual contact or needle-sharing), an HIV p24 antigen test can detect HIV infection seven days prior to the appearance of HIV antibodies. Viral load testing is even more sensitive than p24 antigen testing; HIV RNA can be detected in the blood two or three days prior to p24 antigen. The benefit of HIV RNA testing during suspected acute infection is to reduce the period of diagnostic uncertainty and facilitate very early treatment.

A person who tests positive for HIV in the blood, despite negative or indeterminate antibody results, is said to have primary HIV infection. However, false positive results are fairly common. A viral load result of less than 5000 copies/ml during primary infection is probably suggestive of a false positive result, because most people have viral loads above 100,000 during this time.

There is disagreement among experts about the appropriate use of viral load testing during the early days of HIV infection. Some doctors recommend testing for people with symptoms of seroconversion illness who may have been exposed to HIV. Others are less enthusiastic about the uses of viral testing for asymptomatic individuals with a possible exposure to HIV because of a low yield in actual cases of HIV infection and the risk of false positive results.