HIV antigen/antibody fourth-generation-based screening tests can simultaneously detect both HIV-1 antigen (ie, viral protein) and HIV-1/2 antibodies, whereas HIV-1/2 antibody third-generation-based screening tests detect only antibodies. Third-generation test results are considered repeatedly reactive only after a person has developed detectable levels of antibody in their serum or other body fluid. Because third-generation tests detect only antibodies to HIV, they cannot detect HIV infection during acute infection—the period after virus acquisition when viral protein (HIV-1 antigen) may be detectable but antibodies to HIV are not.4 In contrast, fourth-generation HIV-1/2 testing methods can detect HIV-1 antigen as well as HIV-1 and HIV-2 antibodies.
Thus fourth-generation-based screening tests can detect HIV during a portion of the acute phase and all of the chronic phase of the disease. This ability has substantial individual and societal benefits. The patient benefits in that he/she can be more quickly evaluated for administration of appropriate antiviral medications, which may reduce the adverse early impacts of infection. Society benefits because actions can be taken to reduce HIV transmission. Individuals with acute HIV infection have much higher viral loads, making them more likely to transmit the virus. However, if individuals are diagnosed during the acute phase of the illness, they can be counseled regarding risk-reduction practices and can reduce their viral load with antiviral medication. Both of these actions reduce the likelihood of transmission to uninfected partners.
The CDC recommends using a fourth-generation HIV antigen/antibody test for screening and diagnosis because it can detect HIV during both the acute and chronic phases of infection.5