An HIV test detects immunoglobulins against the virus or the genetic material (DNA or RNA) of HIV in the blood or specimen. P24 antigen, as a HIV core protein, momentarily becomes visible in the bloodstream during the ramp up phase when HIV-1 RNA concentration is increased up to 10,000 copies/mL.
Current rapid diagnostic tests possess high sensitivity and specificity (> 99%) and could be practical for screening individuals as they provide results in 20 minutes or less. A positive rapid HIV test results should be verified with using a supplemental test (namely, Western blot or RNA). The Western blot (an immunoblot test) detects antibodies to viral proteins and it is performed to confirm two positive ELISA tests. This confirmatory test is the gold standard among the diagnostic tests of HIV infection. ELISA is the most common HIV test performed to assay antibodies to HIV. One of the EIA-based tests is p24 antigen. New combined fourth-generation EIA antigen-antibody tests p24 antigen and anti-HIV-1/2 antibodies simultaneously. PCR is used for finding the DNA or RNA of HIV in white blood cells. This technique has high sensitivity and specificity and detects very small number of viral particles.