How they work

The first ELISAs were the first-ever HIV tests and appeared in 1985. They used purified HIV lysates, and often lacked sensitivity and specificity. Second-generation assays based on recombinant proteins and/or synthetic peptides, which also enabled the production of combined HIV-1/HIV-2 assays, became available in the late 1980s.

The so-called third-generation or 'sandwich' ELISAs, which use labeled antigen as conjugate, are extremely sensitive, detect IgM antibody as well as IgG, and reduced the window period considerably.