Enzyme immunoassay (EIA) for antigen/antibody screen for HIV with reflex to supplementary differentiation assay for HIV-1 or HIV-2. The antigen/antibody assay detects antibodies to HIV-1 and HIV-2 as well as HIV-1 p24 antigen. Specimens positive by the screening assay but negative by the supplementary antibody typing assay will reflex to qualitative nucleic acid amplification (NAA).
The fourth-generation HIV antigen-antibody assay is acknowledged to detect acute HIV infection 4 to 12 days earlier than third-generation assays. Coupled with supplemental tests and clinical information, this cascade can help decrease the spread of HIV infection. According to the CLSI guideline, anyone testing positive by a fourth-generation screening assay and supplemental tests (either antibody or RNA detection) should initiate care and follow-up tests for clinical staging.1