HIV Antigen/Antibody Tests
Combination antigen/antibody (Ag/Ab) immunoassays are in their fourth generation for HIV detection and are capable of detecting antibodies against HIV and fragments of the virus itself called antigens. Ag/Ab tests require blood samples (serum, plasma or whole blood) and have the potential to detect a specific protein known as p24 viral core protein, as soon as, three weeks after the initial infection. The p24 particles, however, soon become undetectable once the body speeds up its antibody production and begins to “destroy the evidence” in its fight against HIV. At this point, the second part of the Ag/Ab test becomes valuable, as the antibodies hiding the antigen evidence become reactive to the test allowing accurate detection efforts to continue.
The Western blot (protein immunoblotting IgM IgG) test for HIV is now the confirmatory test preferred by the CDC for double-checking the results of other HIV tests.38 Be aware that the Western Blot may be unreliable in new HIV infections, under two months since time of infection. Also, the Western Blot has difficulty reacting to/detecting the HIV clade “O,” which, though uncommon, is out there.38 Public health regions need awareness of both the type of infection, HIV-1 versus HIV-2 present in their watch areas, but knowledge of the subtypes or clades which are presenting, is important as well.
