From the Guidelines
For HIV screening, the recommended laboratory test is the HIV-1/2 antigen/antibody combination immunoassay, which detects both HIV antibodies and the p24 antigen. This test is preferred as the initial screening tool because it can detect HIV infection earlier than antibody-only tests, potentially identifying infections during the acute phase before antibodies develop 1. The use of this combination assay is supported by the Association of Public Health Laboratories and the Centers for Disease Control and Prevention, which recommend it as the initial screening test for diagnosis of HIV infection 1.
Key Points for HIV Screening
- The HIV-1/2 antigen/antibody combination immunoassay is the preferred initial screening test due to its ability to detect HIV infection earlier than other tests 1.
- If the initial test is reactive, it should be followed by a confirmatory test, typically an HIV-1/HIV-2 antibody differentiation immunoassay 1.
- In cases where the differentiation assay is indeterminate or negative, an HIV-1 RNA test (viral load) should be performed to rule out acute infection 1.
- HIV screening is crucial for early detection and management, with recommendations for all individuals aged 13-64 to be screened at least once as part of routine healthcare, and more frequently for those at higher risk.
Laboratory Diagnosis Approach
The approach to laboratory diagnosis of HIV infection has evolved, with current recommendations emphasizing the use of combination assays that detect both antibodies and antigens 1. This approach allows for earlier detection of HIV infection and can identify individuals in the acute phase of the disease, when viral loads are high but antibodies may not yet be detectable 1.
Importance of Early Detection
Early detection of HIV infection is critical for initiating timely antiretroviral therapy, which can significantly improve patient outcomes by reducing viral loads, preserving immune function, and preventing transmission to others 1. The use of the HIV-1/2 antigen/antibody combination immunoassay as the initial screening test is a key component of this strategy, offering the potential for earlier diagnosis and intervention 1.
From the Research
Laboratory Tests for HIV Screening
The following laboratory tests are recommended for HIV screening:
- HIV p24 antigen test: This test detects the presence of the p24 antigen, which is a protein that makes up most of the viral core [(2,3,4)].
- Anti-HIV-1/2/O screening test: This test detects the presence of antibodies against HIV-1, HIV-2, and HIV-O [(2,5,3)].
- Combination assays: These assays screen simultaneously for both p24 antigen and HIV antibody, reducing the diagnostic window and allowing for earlier diagnosis of HIV infection [(2,5,3,6)].
- HIV RNA testing: This test detects the presence of HIV RNA in the blood, which can be used to confirm the diagnosis of HIV infection [(5,6,4)].
- Antibody differentiation assays: These assays are used to confirm the diagnosis of HIV infection and to differentiate between HIV-1 and HIV-2 [(5,6,4)].
Recommended Testing Algorithm
The recommended testing algorithm for HIV screening includes:
- Initial screening with a combination assay that detects both p24 antigen and HIV antibody [(2,5,3,6)].
- Confirmation of positive results with antibody differentiation assays and/or HIV RNA testing [(5,6,4)].
- Use of HIV viral load testing to diagnose acute HIV infection during the window period 4.