Fourth-generation ELISA tests detect which of the following?

• A. HIV-1 antibodies, HIV-2 antibodies, and p24 antigen
• B. HIV-1 and HIV-2 antibodies
• C. p24 antigen
• D. HIV-1 antibodies and p24 antigen

Answer: (C)

Fourth-generation ELISA tests are designed to detect both HIV antibodies (to HIV-1 and HIV-2) and the p24 antigen in one assay. The p24 antigen is a viral protein that appears in the blood early after infection, often before antibodies are produced, so including antigen detection lets the test identify acute HIV infection sooner than antibody-only tests. Because these assays look for both components, the description that includes HIV-1 and HIV-2 antibodies together with p24 antigen best captures what fourth-generation tests detect. Options that list only p24 antigen or only antibodies miss part of what these tests are designed to measure.