In HIV testing, p24 antigen is described as:

In HIV testing, p24 antigen is described as:

• A. A host antibody
• B. A viral protein detected by some HIV tests.
• C. A cellular receptor for HIV
• D. An enzyme used in testing

Answer: (B)

p24 antigen is a viral protein of HIV—the capsid protein—that can be detected in blood during the early acute phase of infection. The test looks for this viral protein, not for antibodies the body makes. Because p24 appears before the immune system generates detectable antibodies, p24 detection helps identify HIV infection earlier than antibody-only tests. It is not a host antibody, not a cellular receptor for HIV, and not an enzyme used in testing. In practice, many HIV screens combine p24 antigen detection with antibody detection, broadening the window in which infection can be identified and providing earlier diagnosis.

p24 antigen is a viral protein of HIV—the capsid protein—that can be detected in blood during the early acute phase of infection. The test looks for this viral protein, not for antibodies the body makes. Because p24 appears before the immune system generates detectable antibodies, p24 detection helps identify HIV infection earlier than antibody-only tests. It is not a host antibody, not a cellular receptor for HIV, and not an enzyme used in testing. In practice, many HIV screens combine p24 antigen detection with antibody detection, broadening the window in which infection can be identified and providing earlier diagnosis.