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When to test for HIV during and after completion of PEP

I get this question a lot.

First of all, data on this is lacking and very hard to come by.

There are many theories that hypothesize that PEP reduces viral replication and delays sero-conversion and therefore make HIV testing less accurate. These theories have neither been proven nor debunked.

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Furthermore, there is very limited data on the use of P24 antigen tests (including Combo/Duo tests) and viral load testing for diagnostic purposes in patient who have or undergoing PEP. In fact, studies on monkeys (and more limited studies on humans) have shown positive viral load tests in individuals who were subsequently found not to be infected. This could represent an aborted infection (which is what PEP is supposed to and designed to do) rather than a true false positive. This illustrates one of the limitations of using viral load tests to diagnose people currently on or have completed PEP.

Official Guidelines

The US CDC Guidelines on Antiretroviral Postexposure Prophylaxis After Sexual, Injection-Drug Use, or Other Nonoccupational Exposure to HIV in the United States recommends that patients should be tested for the presence of HIV antibodies at baseline, 4 – 6 weeks, 3 months and 6 months post exposure.

The Joint WHO/ILO guidelines on post-exposure prophylaxis (PEP) to prevent HIV infection recommends HIV testing at baseline, immediately after completing PEP (i.e. 4 to 6 weeks post exposure) and again ‘3 – 6 months post exposure’.

The 2 guidelines are rather similar although the US CDC seems to be more firm on the requirement of a test at 6 months compared to the WHO guidelines.

Very recently, the New York State Department of Health AIDS Institute’s adult HIV guidelines committee undertook a comprehensive re-evaluation of its HIV occupational PEP guidelines and issued some changes which included shortening of the time of HIV testing after exposure to 3 months if modern, blood based, standard HIV testing is performed. This is certainly promising however it refers to occupational HIV exposure only and the same data and recommendation may not be extended to non-occupational exposure.

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 In short, most official guidelines still recommend testing at 6 months for patients who have undergone PEP.

Sometimes testing at 3 months post exposure is good enough but this really depends on what kind of test is done.

My own experience is the test done at 4 weeks exposure (or immediately upon completion of the PEP medications) is very indicative. I will still recommend a retest at 3 months although I have yet to see the test at 4 weeks get it wrong.

At the end of the day, the best person to advise you is still the doctor who prescribed you the PEP. He/She will be most familiar with the sensitivity of local tests available and the local guidelines.

HIV Signs and Symptoms

If you have any questions, visit our free online forum on sexual health, HIV and STDs.

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More on HIV symptoms.

If you have any questions, visit our free online forum on sexual health, HIV and STDs.

If you need a HIV test visit Our Clinics anytime during our opening hours. You do not need an appointment.

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If you had a high risk exposure to HIV within the past 72 hours, you can take medicines to reduce your risk of actually contracting HIV. Find out more on HIV PEP Treatment.

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About Dr. Tan
Dr. Tan graduated from the National University of Singapore in 2001. His residency was in the two largest public hospitals in Singapore; Tan Tock Seng Hospital and Singapore General Hospital.

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  1. After late PEP

    I was put on pep 7days after exposure with a HIV partner for 6 weeks.I got a finger prick test at six week mark this is immediately after pep but its 7weeks since exposure. Should I be worried are these results conclusive and indicative?

    • After late PEP

      Forgot to mention the results came non reactive

    • First of all I am shocked that you were given PEP 7 days after exposure. PEP is not useful after 3 days from exposure. Secondly, I do not know what test you did so cannot comment on its accuracy. I suggest you ask the doctor who did the test for you.

      • Thank you for your response. The test I took was Alere Determine Antibody rapid test.Are the odds in my favor?And kindly will late PEP have any effect on my testing for example delaying antibody formation or extension of window period or just any effect

  2. LobsterUP

    Hi doc.

    I had unprotected anal with ejaculation ( i was recepient) and i did bleed after. The sources status was unknown. I went on Truvada and Isentress at 46 hrs after exposure for 28 days. I had negative baseline. 4 weeks after PEP I had negative 4th gen laboratory venous test for antigen/antibody and 8 weeks after PEP it was negative also. I was discharged from further testing. I took a home biosure hiv test at 10 weeks post pep which was negative and had an 11 week post pep hospital test (another hospital) which was negative.

    I’ve only been obsessively worrying as I have had on and off rashes that come and go (along arms or sometimes a few big red blotches on chest) that come and go since finishing pep that has been happening on and off for 13 weeks now.

    Am I conclusive and need not worry?

    • LobsterUP

      Would just like to add I just received a text of Negative HiV again at 13 weeks
      Post pep (17 weeks post exposure) so rashes surely must be unrelated to HIV?

    • Based on your test results, I do not think you have HIV. You may want to get a doctor to take a look at the rashes. I do not think they are related to HIV at all.

      • LobsterUP

        Thanks Doc.

        I went again 19 weeks (15 weeks post pep) for another lab 4th gen test which came back negative. I am finally being referred to a dermatologist. Have been told by nurses I need to put this behind me and stop worrying/testing so I am going to do that now. 7 HIV tests that are negative after PEP should be enough to stop me worrying and 4 HIV specialists and another 4 online specialists (8 HIV experts in total) have all said the same. I’ll leave the rashes with the dermatologist now and see why these have come since the incident/finishing PEP. Thanks again!

  3. Filljose

    Hello doc ,
    I slept with a girl for the first time and our second meeting was in four days time and on that day I knew she was hiv positive . I used a condom which did not break on both occasions .she gave me oral sex on both occasions too . Also she told me she doesn’t not bleed in her mouth as we kissed I do bleed sometimes though .i rushed to my doc who said there was nothing to be worried about . To clear my mind I went to a pharmacist who gave me some arv which I took for 28 days . At I have done the combo test 40 days after exposure and it came negative . Is this result conclusive enough? Also I feel some kind of bites in my throat I am not sure is this is as a result of the medications or it’s a symptom of hiv ? Kindly give your opinion sir .

    • You should have listened to your doctor and not your pharmacist. There was nothing for you to worry about. Officially your test cannot be deemed to be 100% accurate. You need to repeat it at 3 months post exposure.

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