Please explain the difference between 1st, 2nd, 3rd and 4th generation HIV tests?

Q: Could you please explain the difference between 1st, 2nd, 3rd and 4th generation HIV tests?What would an HIV test utilising recombinant antigens be: 1st, 2nd, 3rd or 4th generation? Also, what is an Abbott Axsym test?

A:ELISA, the most commonly performed diagnostic test in developing countries like India, to detect HIV Antibodies (Ab) is classified on the basis of Antigens (Ag) used.1st Generation - used infected viral cell lysate as antigen.2nd Generation - used glycopeptides (recombinant antigens)3rd Generation - synthetic peptides are used as antigens.4th Generation, are the newer tests for simultaneous detection of p24 Ag (HIV-1 Ag) and HIV-1/HIV-2Ab.HIV tests utilizing Recombinant antigens would be 2nd Generation. Abbot AxSYM test is a 3rd Generation test.