From the Guidelines
The recommended test for diagnosing HIV infection is a combination approach starting with a fourth-generation antigen/antibody immunoassay, followed by confirmatory testing if the initial test is reactive. This approach is supported by the most recent and highest quality study 1, which highlights the importance of early detection and treatment initiation. The two-step algorithm begins with a blood test that detects both HIV antibodies and the p24 antigen, allowing for earlier detection of infection compared to antibody-only tests.
Key Considerations
- If the screening test is positive, a confirmatory test such as an HIV-1/HIV-2 antibody differentiation immunoassay is performed to verify the result and distinguish between HIV-1 and HIV-2 infections.
- In cases where the differentiation assay is indeterminate or negative despite a positive screening test, an HIV RNA test (viral load) should be performed to detect acute infection.
- This testing approach can identify HIV infection as early as 2-3 weeks after exposure, which is crucial for early treatment initiation.
- Early diagnosis allows for prompt antiretroviral therapy, which prevents progression to AIDS, reduces transmission risk, and leads to better long-term health outcomes.
Testing Recommendations
- Testing is recommended for all adults at least once in their lifetime, with more frequent testing for those with ongoing risk factors.
- The conventional serum test for diagnosing HIV infection is the repeatedly reactive immunoassay followed by confirmatory Western blot or immunofluorescent assay, but the fourth-generation antigen/antibody immunoassay is preferred due to its earlier detection capabilities 1.
- Rapid HIV testing may use blood or oral fluid specimens and can provide results in five to 40 minutes, but initial positive results require confirmation with conventional methods 1.
From the Research
HIV Testing
To diagnose HIV infection, the following tests are recommended:
- Fourth-generation HIV antigen-antibody combination assays, which can detect both HIV antibodies and p24 antigens 2, 3
- p24 antigen tests, which can detect the p24 protein of the virus 4, 5
- Nucleic acid amplification tests (NAATs), which can detect the genetic material of the virus 3
Test Characteristics
The characteristics of these tests include:
- High sensitivity and specificity for detecting HIV infection 2, 3, 4
- Ability to detect HIV infection earlier than antibody-only tests 2, 3, 4
- Importance of using a combination of tests to confirm diagnosis 3, 5
Specific Tests
Some specific tests that have been studied include:
- The Elecsys HIV combi PT assay, a fourth-generation HIV antigen-antibody combination assay 3
- The Determine HIV 1/2 Ag/Ab Combo test, a rapid antigen and antibody combination test 4
- The HM-ELISA+PSAM test, an ELISA with a photochemical signal amplification system for detecting HIV-1 p24 antigen 6
Key Findings
Key findings from the studies include:
- The importance of early detection of HIV infection for public health and diagnostics 2, 3, 4
- The need for ongoing evaluation of HIV diagnostic tests to ensure they remain effective against diverse HIV subtypes 2
- The potential for p24 antigen tests to detect HIV infection earlier than antibody-only tests 4, 5