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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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Summary

 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.

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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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631 Comments

  1. Gary Summers

    Doc,

    I am wondering the rationale for those on PEP testing -ve four weeks after exposure (immediately after PEP) not going on to become +ve later. I would think that due to PEP, viral replication is subdued, resulting in subdued antigen production and hence subdued antibody production. However, once PEP is removed, antibody production is resumed and it will come out to be +ve a few weeks after PEP. The only scenario in which it would be +ve immediately after PEP is when the virus is resistant to PEP drugs and continues to replicate despite PEP.

    Is there a flaw in my logic here? Thanks.

    • That is sound logic but it is not proven by science. There are many things in the body and immune system we do not understand. Example: Why do some people infected with HIV never develop any antibodies? I often warn my patients against trying to figure out their status though “logic”. It never works. Just test.

      • Gary Summers

        Thanks Doc. I tested immediately after PEP using 4 Gen Combo and it was negative. However the symptoms which I experienced are so textbook like without any other possible explanation that I am a bit apprehensive. Nonetheless I will test as per recommended guidelines in 2 months from PEP completion and keep fingers crossed. Thanks.

  2. HI I had sex for the first time with csw on 10thsep. I used condom both the times for vaginal intercourse. apart from that we had kissing touching & hand job. I didn’t remember if the condom breaks as I just removed it and throw it off in dustbin without checking.Now I am bit feverish and diaorreah. I am planning to for 4th gen HIV test on 26th sep. Please let me know how conclusive it will be

    • That is only 16 days after exposure. Your test will not be conclusive. You can consider doing the RNA PCR test for better accuracy. Please check with your doctor. You are welcome to visit any one of our clinics.

  3. Hello,

    A girl gave me an unprotected oral sex 53 days before. I was fear to be infected HIV, so I went to a clinic to have some following tests:

    Day 14 PCR (Negative)
    Day 30 HIV Combo Test (Negative)

    Can I ask those tests are conclusive or not? I am still worried about it everyday. Also, my skin is tunning to be sensitive in these recent day. Is it related to HIV?

    Looking to your reoly soon.

    Jackson

    • In my opinion your tests are conclusive. However, the best person to advise you on the accuracy of your tests is the doctor who did the tests for you.

  4. Gary Summers

    Doc,

    I had a related question and would appreciate your reply. I had an exposure about 3 weeks back. I came down with strong symptoms (chills, feverish feeling but no high temperature (<37.6 degree), very bad sore throat, fatigue, loss of appetite, weight loss of 2-3kg) from day 3-7 after exposure. Since then I have been recovering but there's still some sore throat, fatigue and joint pain. I immediately got myself on PEP after 60 hours of exposure when I first started to feel a bit unwell.

    While I understand any test during PEP is non conclusive, 3 weeks after exposure (18 days after starting PEP + 18 since my symptoms started) I did a HIV Combo test (4 Gen – p24 antigen / antibody with window period of 14 days) with the rationale that if my symptoms were related to ARS, then this test should come out to be positive. However, the test is negative. Would appreciate your thoughts on the efficacy on the test. Thank you.

    • Your symptoms came on much much much too early to be due to HIV ARS. There is no good data on the accuracy of the Combo test during PEP.

      • Gary Summers

        Thanks for your reply doc. I finished my PEP yesterday and have tested negative on 4th Gen HIV Combo (p24 antigens and antibodies ELISA) today. While I understand it’s not conclusive, is it a reasonable indication in your opinion?

  5. Thank you for your reply Dr. My main concern is the rash i developed which happened 2 weeks post exposure. My doctor diagnosed it as folliculitis but he saw it several weeks after. To me the rash looked maculopapular with “small pimples”. Also, my other concernis that my wbc was 15 and lymphocytes down to 15%. Would you still believe that this is not link to ars and my results have been negative because of pep. Do you recomend to test again in 6 months? Or you truely believe that the 11 week duo and 12 week rna are conclusive? Thank you again for your help

  6. Hello Dr.

    I had an unprotec exposure on 6/10 with someone who is positive. I went on pep at 44 hrs after exposure. A few weeks after I developed a rash which I never had before and swollen lymph nodes. I also have had night sweats, my palms are always warm now and I had a lip blister. I had extensive testing but everything has come out negative.

    I have had the following tests

    Duo and DNA 5 days post exposure
    Duo 5 days before end of pep
    Duo and RNA 3.5 after pep/7.5 weeks post exposure
    Duo 7 weeks after pep/ 11 weeks post exposure
    RNA 8 weeks after pep/ 12 weeks post exposure

    I also had a WBC which was elevated. Do you believe this is a sign of acute infection? When should I test again? How reliable are my results ?

    • I forgot to mention that I also have blurred vision and that my rash occurred on my back and dr diagnosed it as folliculitis – which I never had before. Thank you for any advice you could provide. Im going through the worst days of my life.

      • Would you consider the RNA and duo at 8 weeks post pep a good indicator of my status despite my symptoms?

        • Personally, I do not think any of your symptoms are suggestive of a HIV infection and that your tests are all as good as conclusive. Please follow up with your doctor.

          • Thank you for your reply Dr. My main concern is the rash i developed which happened 2 weeks post exposure. My doctor diagnosed it as folliculitis but he saw it several weeks after. To me the rash looked maculopapular with “small pimples”. Also, my other concernis that my wbc was 15 and lymphocytes down to 15%. Would you still believe that this is not link to ars and my results have been negative because of pep. Do you recomend to test again in 6 months? Or you truely believe that the 11 week duo and 12 week rna are conclusive? Thank you again for your help

  7. 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

  8. 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!

      • LobsterUP

        Had negative results at 23 weeks post exposure (19 weeks after pep completion), can I consider myself conclusive?

        Still getting clusters of non-itchy red spots (no other symptoms) on the back of my hands or wrist area that come and fade occasionally… Not sure if im still suffering from
        Some type of allergy rash from the medication. My dermatologist appt referral is a 22 week wait.

  9. 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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