From the Guidelines
After two false positive HIV tests, a Western blot or HIV RNA PCR test should be run for confirmation, as recommended by the most recent guidelines 1. These tests provide higher specificity than the initial screening tests and can definitively rule out HIV infection. The Western blot identifies specific antibodies against HIV proteins, while HIV RNA PCR directly detects viral genetic material in the blood. False positive results on screening tests can occur due to cross-reactivity with other antibodies from conditions like autoimmune diseases, recent vaccinations, or pregnancy. It's essential to complete this confirmatory testing before making any diagnosis, as false positive HIV results can cause significant psychological distress and potentially lead to unnecessary treatment. The confirmatory test results should be interpreted by a healthcare provider experienced in HIV diagnosis who can explain the findings and recommend appropriate next steps based on the complete clinical picture. Some key points to consider when interpreting these results include:
- The time course of test positivity, with HIV RNA positivity typically preceding antibody detection by several days 1
- The possibility of seronegativity in acute HIV infection, making HIV RNA testing a useful diagnostic tool in this setting 1
- The importance of using fourth-generation assays that incorporate HIV p24 antigen detection for earlier diagnosis of infection 1
- The recommendation to use combined HIV antibody plus p24 assays as initial screening tests, followed by further testing with an antibody immunoassay that distinguishes HIV-1 from HIV-2 antibodies 1
From the Research
Follow-up Testing for False Positive HIV Results
After two false positive HIV tests, it is essential to conduct further testing to confirm the results. The following are some options:
- Nucleic Acid Test (NAT): This test can detect the presence of HIV genetic material in the blood and is considered a reliable method for confirming HIV infection 2, 3.
- Western Blot: This test is a confirmatory test that can detect the presence of HIV antibodies in the blood. However, it may not be as sensitive as NAT, especially in early stages of infection 4, 3.
- Fourth Generation ELISA: This test can detect both HIV antibodies and p24 antigens, making it a more sensitive test than traditional ELISA 3.
- Sequential HIV Serological Testing: This approach involves using a combination of tests, such as ELISA and Western Blot, to reduce false-positive results 5.
Considerations for Testing Algorithms
When choosing a testing algorithm, it is crucial to consider the prevalence of HIV in the population being tested. In areas with low HIV prevalence, the use of NAT or fourth generation ELISA may be more effective in reducing false-positive results 2, 3. Additionally, the testing algorithm should be evaluated and reviewed regularly to ensure that it is effective in detecting HIV infection while minimizing false-positive results 5.