A concern during the early AIDS epidemic was the lack of a test to identify 
individuals who carried the virus. The first HIV antibody test, developed in 
1985, was designed to screen blood products, not to diagnose AIDS. The 
first-generation assays detected IgG antibody and became positive 6 to 12 weeks 
postinfection. False-positive results occurred; thus, a two-test algorithm was 
developed using a Western blot or immunofluorescence test as a confirmatory 
procedure. The second-generation HIV test added recombinant antigens, and the 
third-generation HIV tests included IgM detection, reducing the test-negative 
window to approximately 3 weeks postinfection. Fourth- and fifth-generation HIV 
assays added p24 antigen detection to the screening assay, reducing the 
test-negative window to 11 to 14 days. A new algorithm addressed the 
fourth-generation assay's ability to detect both antibody and antigen and yet 
not differentiate between them. The fifth-generation HIV assay provides separate 
antigen and antibody results and will require yet another algorithm. HIV 
infection may now be detected approximately 2 weeks postexposure, with a reduced 
number of false-positive results.