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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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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. Hi Dr Tan,

    Congratulations for website, very good informations.

    I’ve be exposed to a risk and started a PEP 36 hours after the risk (anal sex eith girl that unknown her status – condom broke)

    I’ve been tested ad the following:
    – before PEP: 3 generation test (negative)
    – 40 days after risk (10 days after pep): 3 generation negative
    – 60 days after risk (30 days after pep); 4 generation + p24 negative

    It’s strongly recommend perform test again within 90days after risk or the case can be considered closed (my medic here in Brazil has considered closed the case).

    Sorry to ask this kind of question, but I’m little worried that outside of Brazil they request test till 3 months after risk.

    Thank you in advance


    • Different counties and health authorities have different guidelines on when to test conclusively after PEP. I have shared some information in the article above. For your particular situation, you should seek and listen to the advice of your local doctor.

  2. Hi Dr Tan, is a 4th gen test(antigen/antibody) 3 weeks post-exposure whilst still on pep of any use?

    • I honestly do not know how to answer that question. What do you mean “of any use”? It will not be conclusive.

  3. Hi Dr. Tan

    after a low risk exposure (protected sex), i finished PEP and then took a CMIA combo test 3 months post exposure (i.e. 2 months after PEP)

    The result was non-reactive: http://tinyurl.com/j4sojds

    Is this considered as conclusive?

    • PEP guidelines recommend between 3 to 6 months post PEP testing. Please verify with your local doctor what your local guidelines say. We cannot comment on the accuracy of your results. You should verify this with the doctor who did it for you.

  4. Hello doctor. Finished my pep 28 days regime. 5 days after finishing pep 4gen antigen and antobdy testing was negative.

    1. Is it conclusive?

    2. Does a 4 gen antigen and antibody test will be conclusive after 6 week post pep ?

    Thank you

  5. Hi.Dr.Tan i am sara 24 yrs I got pricking while giving cannulation around 3:30 pm and splashing of blood in my fingers for a few drops i.e around 5:30 pm from a patient who had HBsAg and HIV1&2 reactive then after I consult with the Doctor he prescribed me PEP tx i.e tabs.Duovir for 28 days….so I have done test only hepBantibody so Sir will you advice me something cause m really scared tensed Sir

    • I am not sure what kind of advice you are looking for. You had an occupational exposure (I am sorry to hear that) and your Doctor has very intelligently and responsibly put you on PEP. You will just have to finish your PEP and get tested according to your hospital’s protocol. I wish you all the best.

  6. testafterpep

    Dr Tan, After a condom break exposure I took PEP within 24hrs. On the 30th day I tested using a 4th gen combo test and result was negative. Am I in the clear now?

  7. Weekend gettogether

    Hi Doc
    I had a weekend of lot of unprotected intercourse of which I bled after each intercourse with my boyfriend then we tested on Sunday morning of which he tested positive and me negative I then took pep 33 hours later from first exposure . will Pep be effective thou there was too much bleeding and too much hiv exposure

    • As far as I know, the 2 factors you brought up does not affect the efficacy of PEP.

  8. PEP testing

    Hi doctor,

    Thank you for the wonderful work you all do in reaching out to us.

    My scenario is that I had unprotected vaginal sex with a commercial sex worker. Went on PEP 48 hours after exposure and completed the treatment. Now 2 weeks after pep/ 6 weeks post exposure I did a SD bioline combo test. Results were negative.
    1) I would like to ask if this is conclusive?
    2) should I be worried still, since you have not seen a result at 6 week post exposure turn positive later on at 3 months?

    • 1. IMHO yes but verify with your doc.
      2. I do not know how to answer this question.

  9. Hi Dr. Tan

    I had a low rise exposure (condom was used & Intact). 60 hours post this, i took PEP (started with Duovir+Efavir for 1.5 days and the switched to a 30 day Isentress+Tenvir regimen because of efavir side effects) and completed that course.

    16 days after completing PEP (i.e. 51 days after exposure), i tested non-reactive on a 4th generation test.

    1) Is the 51 day post exposure near conclusive?

    2) In this test, the ELFA index value was 0.2 and non-reactive (cut off value as per report is 0.25). But the index value of the test i took before starting PEP was 0.02 and Non-reactive. Is this something to worry that the value has risen sharply over 6-7 weeks?

    I anyway plan to do another test at the 3 months post exposure mark. But am so worried that the index value is so close to the cut-off value of 0.25. Please advise.

  10. Hi doc Tan,

    Have a couple of questions, am a patient at your katong branch wanted to check with doc Jess however she is away this weekend so I can’t have answers to my question.

    I have completed my pep treatment today is day 33 post exposure, 2nd day since completing pep. On day 33 post exposure I did a anonymous sd bioline combo test which was negative. Is this conclusive or perhaps a good indicator that there is no HIV since your experience indicates that the 4th week test have not got it wrong at 3 months too?

    • In my view as good as conclusive. I am sure your test at 3 months will be clear too.

  11. hi dr tan i had sex with sex worker and i used pep for 29 days after that at 6 week post expouser hivab/ag negeative since then i did due test every week until 13 week that it was hiv ab/ag non reactive so after 13 week is this test realiable? i did pcr test but i am waiting for the test result but can i be sure after 13 week?

    • Generally speaking I can say your tests are conclusive. However, there are many testing details I am not privy to. Therefore you should still verify the accuracy of your tests with your doctor.

      • hi dr tan tnx for your answer i get pcr test negative after 3 month so can i be relax?

  12. hi dr tan i had sex with sex worker and i use pep after 3 month i get hiv ab/ag test last week it was .364 this week was .371 the number goes up but its non re active so after 3 month is this test reliable?

  13. Dr Tan,

    I did a 4 Gen Combo test (lab) and RNA PCR test (<100 copies / ml) four weeks after finishing PEP. I continue to suffer from symptoms such as pain in the neck, oral blisters and malaise. Are these tests practically conclusive in your view?

    Is it possible the PEP suppressed viral load to undetectable even 4 weeks after finishing the last dose?


  14. Hello Sir, I had unprotected sex with a sex worker, although she said she was not +ve, after that I quickly went to doctor and he assigned me tablets of “viraday” for 30 days.I started using it within 11hrs of exposure. I tested -ve after 3 and half months of exposure, should I test again after six months of exposure, coz I had pep for 30 days..?
    Please help me sir..

  15. You mention after PEP … test taken 3 months post exposure is good enough but really depends on what kind of test is done… Can you pls clarify which tests you think meet this criteria. anxious
    Y waiting for my 3 month post exposure 2 month post PEP test and want to ensure I take the right test

  16. Dear Dr,
    I had risk exposure on 26/7/15. I took PEP between 68 to 72 hours post exposure. I finished the course. I had negative result 5 weeks after risk exposure, 1 week after completion of PEP. I had negative anti-HIV 1/O/2 results 22 weeks or 5 months post risk exposure. Please advise of my next tests if necessary. Thank you.


  18. Forget to mention if below points help
    consider that the receptive male sex worker is positive( may be high viral load as many sex workers dont use medicines and treatment).
    2) I do stupid stuff like washing penis with antiseptic and then with hot water cause any high risk?
    3) is my PEP dose correct and timely started? as i dint take any other thing like injection or liquid medicine at start, i just started with tablets.

    Points to be consider if they may help you in analysis and answer to me.
    1) Male sex worker may be HIV+
    2) MY WBC count at that time was 11000( i done health checkup few days before the incident)
    3) I was drunk( but i remember everything that unprotected time is less than 5 seconds)
    4) I am uncircumcised.

    • 1. This will not make any difference.
      2. Yes, it is effective if taken within 72 hours.

      If you are extremely concerned, you can do a HIV RNA PCR 10 days from exposure. However, the result may not be very accurate. Best time to check is 1 month from exposure.

  19. First of all thanks for the wonderful work you are doing.
    Please consider my case as urgent.
    I am a 29 year man, I had sex with a Male sex worker in mexico on 2 October 2016 , I Put my condom and push my dick inside his ass( no kiss and other activity) but condom break during pushing my dick go inside but I quickly withdraw my penis and wash it with anticipate lotion( without water) clean it with soft towel and this time i put 2 condoms on penis and again start sex,i come inside him this time no condom break. The unprotected encounter was for only one jerk. I wash my penis with HOT water and clean it with tissue paper. I was having fear so i go to a hospital and asked for pep but that was Sunday so i could not PEP, next day i started PEP ( after 28 Hours ) The pep was 1 tab of truvada( per day) and 2 tab of kaletra( twice in a day). I am having Truvada + kaletra in morning after Breakfast and kaletra in Night after dinner. I did not miss any dose till day 10. What is the chance of Getting HIV. When i should get test ( As early as possible test).My PEP will finishon 2 nov 2016.

  20. Gary Summers


    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.

  21. 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.

  22. 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.


    • 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.

  23. Gary Summers


    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?

  24. 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

  25. 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

  26. 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

  27. 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.

  28. 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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