PEP Treatment: When to Test for HIV Infection

Questions regarding testing after Pep administration?

Hello Doctor, I apologize for the interruption.
I started Post-Exposure Prophylaxis (PEP) on June 11 due to engaging in high-risk sexual behavior and completed the full course of medication on July 8.
However, I mistakenly had unprotected oral sex a few days later, which led to concerns, so I began another round of PEP on July 12 and completed that on August 8.
I started counting 28 days from August 8 and went for a Combo ELISA rapid test and a blood test at the hospital on September 11 and September 12, respectively, both of which returned negative results.
I have a few questions for you, Doctor.
Does this mean that both rounds of PEP were successful and that I can confidently rule out infection? Additionally, I am confused about how long after PEP treatment I should wait to get tested to rule out infection.
I have looked up various hospitals and organizations online, but the responses vary.
Some say that the window period for antigen and antibody testing is only 2-3 weeks (with a conservative estimate of 4 weeks), and that the window period for RT-PCR testing is only 1 week.
As an infectious disease doctor mentioned, the concentration of the medication in the body decreases quickly after stopping the treatment, so the window period can be counted from the end of the medication, and undergoing one of the tests is sufficient.
Current screening technologies are widely available and accurate, so there is no need to conduct multiple tests or repeat testing (according to the HIV Rights Promotion Association).
Others state that an initial blood test for HIV antibodies should be done after exposure, and subsequent tests should relate to the fourth-generation HIV COMBO test, indicating that testing can be done 3-4 weeks post-infection, eliminating the need for the previous 3-month follow-up, thus theoretically shortening the follow-up period for PEP (Taoyuan Hospital).
Yet, some say that blood tests are required at 6 weeks and 12 weeks after starting medication, and if the 12-week test is negative, it can confirm that infection is ruled out.
Therefore, I would like to ask you, Doctor, how long after PEP treatment should testing be conducted to rule out infection, and which of the aforementioned information can I trust? Thank you for your assistance, Doctor Hong.

Ke Ke, 20~29 year old female. Ask Date: 2019/09/24

Dr. Hong Yuanbin reply Internal Medicine

Hello, this question indeed does not have a standard answer because currently, there are different practices internationally based on various studies and treatment guidelines, including the use of different reagents, which can affect sensitivity.
Therefore, each hospital will have different recommendations based on the specific testing reagents they use.
However, most hospitals' practices will be similar to those of Taoyuan Hospital.
You may refer to the relevant information from the Centers for Disease Control (CDC) at https://www.cdc.gov.tw/Category/QAPage/My0uZvjAFs11NWjujWXvBg.
Thank you for your inquiry.

Reply Date: 2019/09/24

More Info

When it comes to Post-Exposure Prophylaxis (PEP) for HIV, understanding the timing of testing for HIV infection is crucial for peace of mind and health management. Based on your situation, you began PEP treatment on June 11 and completed it on July 8, then started another round of PEP on July 12 and completed it on August 8. You subsequently tested negative for HIV using both the Combo ELISA test and a blood draw on September 11 and 12.

Understanding PEP and Testing
PEP is a preventive treatment that can significantly reduce the risk of HIV infection when taken within 72 hours after potential exposure. The effectiveness of PEP is highest when it is started as soon as possible after exposure and taken consistently for 28 days. The fact that you completed two full courses of PEP is a positive sign in terms of reducing your risk of infection.

Testing After PEP
Regarding your question about when to test for HIV after completing PEP, the general guidelines suggest the following:
1. Initial Testing: After completing PEP, it is advisable to have an initial HIV test at approximately 4 weeks (28 days). This is because the body may take time to produce detectable antibodies or antigens after exposure.

2. Follow-Up Testing: While some sources suggest that testing can be done as early as 3-4 weeks after exposure, it is often recommended to have a follow-up test at 3 months (12 weeks) to conclusively rule out HIV infection. This is due to the possibility of the "window period," where the virus may not be detectable immediately after infection.

3. Types of Tests: The Combo test (which detects both HIV antibodies and the p24 antigen) is considered highly reliable and can provide results sooner than antibody-only tests. RT-PCR tests can detect the virus itself and are effective within a week of exposure, but they are typically used in specific clinical situations rather than routine screening.

Interpreting Your Results
Given that you tested negative at 9 weeks after your last PEP course, it is a strong indication that you are likely not infected with HIV. However, the recommendation for a follow-up test at 12 weeks remains prudent, especially considering the potential for any late seroconversion.

Conflicting Information
You mentioned encountering various recommendations regarding testing timelines after PEP. This discrepancy often arises from differences in clinical practices, the types of tests used, and individual patient circumstances. Generally, the most conservative approach is to follow up with testing at 12 weeks after the last potential exposure or after completing PEP.

Conclusion
In summary, based on your negative test results at 9 weeks post-PEP, it is reasonable to feel reassured about your HIV status, but a follow-up test at 12 weeks is advisable for complete peace of mind. Always consult with your healthcare provider for personalized advice, as they can consider your specific situation and any additional risk factors. Remember that maintaining open communication with your healthcare provider is key to managing your health effectively.

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