ELISA for anti-HIV uses a 4th generation (combination) format. What makes 4th generation ELISA superior to 3rd generation for early HIV detection?

• A Using recombinant HIV gp120 and gp41 antigens instead of viral lysate
• B Adding HIV-2 specific antigens to detect both HIV-1 and HIV-2 antibodies
• C Detection of both HIV p24 antigen and anti-HIV antibodies simultaneously, reducing the diagnostic window period ✓
• D Using sandwich format instead of indirect format to increase sensitivity

Explanation

4th generation HIV combo assays simultaneously detect HIV-1/2 antibodies AND HIV p24 antigen in a single test; p24 antigenemia appears as early as 2 weeks post-infection (before antibody seroconversion), so detecting both reduces the window period (time between infection and positive test) from ~3-4 weeks (3rd generation) to ~15-18 days; this is critical for blood bank screening and early diagnosis. 3rd generation assays use recombinant antigens and detect IgM+IgG but not p24. Both 3rd and 4th generation assays detect HIV-1 and HIV-2 antibodies. Sandwich format is used in both generations for antigen capture.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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