Can an HIV (Human Immunodeficiency Virus) test result turn positive at 90 days if it was negative at 83 days with a 4th generation test and negative qualitative PCR (Polymerase Chain Reaction), after taking Post-Exposure Prophylaxis (PEP) with antiretroviral medications such as tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC)?

From the Guidelines

It is extremely unlikely for an HIV test to turn positive at 90 days if it was negative at 83 days with both a 4th generation test and a qualitative PCR, especially after completing PEP with TDF and FTC. The 4th generation HIV tests detect both antibodies and the p24 antigen, allowing detection as early as 2-3 weeks after exposure, while HIV RNA PCR tests can detect the virus even earlier. By 83 days (approximately 12 weeks), these tests provide highly reliable results with over 99% accuracy 1. PEP with tenofovir disoproxil fumarate and emtricitabine, when taken properly within 72 hours of exposure and completed for the full 28-day course, significantly reduces the risk of HIV infection. The window between 83 and 90 days is not clinically significant for seroconversion if proper testing was already performed. Some key points to consider include:

• The high sensitivity of modern HIV testing methods at the 12-week mark makes additional testing at 90 days generally unnecessary for most individuals 1.
• PEP regimens should be continued for 28 days, and HIV serostatus should be reassessed at 4 to 6 weeks, 3 months, and 6 months after exposure, although shorter follow-up may be possible with a fourth-generation assay 1.
• The use of TDF/emtricitabine as part of PEP is recommended, with options for adding other medications based on the specific circumstances of the exposure and the individual's health status 1. For complete reassurance, some clinicians might recommend a final confirmatory test at 3-6 months post-exposure, but this is generally considered excessive given the high sensitivity of modern testing methods at the 12-week mark.

From the Research

HIV Test Results and PEP

• The question of whether an HIV test result can turn positive at 90 days if it was negative at 83 days with a 4th generation test and negative qualitative PCR, after taking Post-Exposure Prophylaxis (PEP) with antiretroviral medications, is complex and depends on various factors.
• Studies have shown that PEP can be effective in preventing HIV infection, but its effectiveness depends on adherence to the treatment regimen and the timing of the exposure 2, 3.
• A study published in 2020 found that using a point-of-care PCR HIV test in individuals attending for PEP could potentially shorten the testing window period and pick up early infections that would be undiagnosed by conventional tests 4.
• However, another study published in 2012 found that pre-exposure prophylaxis with antiretroviral drugs did not significantly reduce the rate of HIV infection in African women, and was associated with increased rates of side effects 5.
• The use of tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) as PEP has been shown to be effective in preventing HIV infection, but the risk of viral resistance and reduced condom use are potential drawbacks 6.

Window Period for HIV Diagnosis

• The window period for HIV diagnosis refers to the time between exposure to the virus and the appearance of detectable antibodies or viral load in the blood.
• The 4th generation HIV test can detect HIV infection earlier than previous tests, but it may still miss early infections 4.
• Qualitative PCR tests can detect HIV RNA in the blood and can potentially shorten the window period for diagnosis, but they may not be as sensitive as quantitative PCR tests 4.
• The study published in 2020 found that using a point-of-care PCR HIV test in individuals attending for PEP could potentially shorten the testing window period, but it did not find any additional HIV infections that would have been missed by conventional tests 4.

PEP and HIV Test Results

• PEP can affect HIV test results, as antiretroviral medications can suppress viral replication and delay the appearance of detectable antibodies or viral load in the blood.
• A study published in 2019 found that PEP with TDF/FTC/RPV was effective in preventing HIV seroconversion, and no HIV seroconversions were observed at week 16 3.
• However, the study did not address the question of whether an HIV test result can turn positive at 90 days if it was negative at 83 days with a 4th generation test and negative qualitative PCR, after taking PEP.
• It is essential to note that there is no direct evidence to support the idea that a negative HIV test result at 83 days can turn positive at 90 days after taking PEP, but it is crucial to follow the recommended testing protocol and consult with a healthcare professional for personalized advice 2, 3, 4, 6, 5.