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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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796 Comments

  1. Age:40, Gender: Male

    Hi,
    I had unprotected test 5weeks ago with sex worker , I mat doctor after and he suggested gualtive pcr hiv1 and p24 combo and hc and hb
    also all three result came bake negative.

    my question is after 5 week is both test are cinfrimativ or not becuase my doctor said you dont requiredw more test.

    but from 8week I am geeting some pimple on my arms and face is this is related to early hiv symptoms.

    Thanks,

    • I would say the HIV test is conclusive but Hepatitis B & C may take another 2 months to be fully conclusive. Your pimples are not due to HIV.

  2. aylliaute

    Hi dr, first thank you for for the time you spent to answer the questions in here.
    I’ve read your post and the comments carefully, and here is mine :

    Of course this is my understanding, an it might be false!
    It’s said that a test right after the completion of pep should already be a really indicative result, meaning pep isn’t delaying seroconversion.
    Anyway, if pep is somehow designed to supress the hiv virus in the blood, there should be no hiv in the blood and therefore no production of antibodies. And so (if infected) the production of the antibodies would start at the end of the pep-28 days, meaning a test right after the completion could really come negative although a seroconversion (AB production) is yet to come.

    Is this is true, how could a test right after completion be really indicative ?
    I’m just asking as I tested negative one day after finishing pep, but can’t determine how reassuring that result should be. In a few days I’ll do my ~20days post pep test

    Also a last thing, my exposure was receptive oral sex on a homosexual sexworker. It’s said that the risk is higher if it exists an other STD, but what’s the exact meaning of this? That if I was already infected with an other STD the risk is higher, or that if during the intercourse I’ve been contaminated with an STD then the risk of hiv transmission
    is higher?

    Two days after finishing pep an infection started in my throat, like a second uvula. Would that be possibly linked to an hiv infection? Or is there an std that could possibly give me that symptom?

    Thank you a lot and sorry of the long message, I’m looking forward to your opinion on thoses questions

    Best regards!

    • PEP does not delay seroconversion. You would still have HIV antibodies produced if you were infected. There have been no documented cases of a negative test after PEP turning positive later on if it was taken properly and there were no other high risk exposures during PEP. The guidelines for a repeat test 3 months post-exposure are precautionary. In any case, your initial exposure is close to zero risk.

  3. Steve S

    Would Atripla have same effect on window period as pep? Or would it be more likely to cause a delay in antibodies?

    If somebody took Atripla 4 weeks after exposure would it have any effect on antibodies production?

    • Steve S

      Sorry for asking again but my original questions disappeared and I though they got deleted somehow, didn’t mean to ask essentially the same question. Please respond I am going crazy, already lost my job and probably my wife over my anxiety.

      • Please see a psychiatrist. HIV is not the problem, only your anxiety.

        • Steve S

          I am seeing a psychiatrist, I want to put this behind me. I just can’t get over the positive p24 test. Also when this first happened my cd4/cd8 count was inverted, that was after 11 days on Atripla. I’ve read inverted cd4/cd8 is very unlikely outside of hiv.

    • Atripla does not affect the window period or antibody production.

  4. Steve S

    PLEASE HELP. I tested positive on p24 portion of a test. I was put on Atripla that day. On the 11th day after starting Atripla I was undertake. I stopped Atripla on 18th day dr said it was false positive. Since then I have taken many test all negative or undetectable. My last viral load test was 7 1/2 months after stopping Atripla. My last antibody test was 8 months and 3 weeks after stopping Atripla. My risks was 4-6 weeks prior to testing positive. Also had a risk approx 15 years ago. Multiple Drs have told me I’m negative but I am still scared. Could the Atripla have made me undetectable and could it have delayed my anitivody response? Could I have no antibodies because I’ve been infected for 15 years? Please help I want to move on from this nightmare.

    I was given a confirmation test but dr admitted they gave me an antibody only and by the time they realized their mistake I was already on Atripla for 11 days.

    • You should listen to your doctors as they are the ones who have performed your tests and know your clinical situation. Overall what we can say is that false positive results happen. With multiple negative results thereafter, by definition you do not have HIV.

  5. Dear Dr. Tan,

    I completed 30 days of PEP prescribed at your clinic, did an Elisa ag/ac duo combo test 4 months after exposure, 3 months after treatment. It came back negative. Is it conclusive? Can I move with my life?.

    Thank you so much

  6. Philospher

    Dear doctors,

    That’s my situation: receptive anal intercourse after a condom broke. The Partner of unknown serostatus refused to test.
    I went to the hospital the day after.
    1) 4th generation test at baseline Negative.
    Local hospital prescribed PEP after 24 hours. I went on for 28 days.
    2) 32 days after exposure (4 days after PEP), 4th generation test Negative.
    After sore throat I did another test:
    3) 25 days after PEP, 4th generation test Negative.
    Would you consider these quite conclusive? I know that 3 months post exposure will be conclusive, but I’d like to ask you an opinion.
    Many thanks

  7. Dear Sir,
    I tested after Eight week post PEP with fourth generation Elisa,Negative.
    But results was published within 6 hours after blood was taken. Equipment they used was Bio Rad genscreen ultra ag/ab. But here somewhere in Internet found it will take seven days for result to come with fourth generation elisa. Shall I be assured the test they took was fourth generation. I also asked them they said it’s 100 percent fourth generation.time does not matter for test to come???

    • I cannot tell you what test the lab did. There is no way for me to know. 4th Gen tests can be done in as little as 20 minutes.

      • Dear Sir,
        Lot of thankful appreciation for the reply. I just need your words to move on. I did fourth generation Elisa Ag/ab after exactly 12 week of exposure, 8 weeks of PEP, negative but before this mark only rapid tests all negative. Lot of weight loss and fatigue during this period. I have followed all your recommendations for testing and PEP but due to lack of knowledge I did all rapid test before final test on 12 week mark. I m so much stressed. Just a words sir..!!

  8. Lucas_H

    Hi Doctors

    I will keep it short and simple or try’s to not to waste your time. I had an exposure with a HIV+ person 18 days ago. I was given PEP two days later and have been taking it since. I went for a HIV PCR Qualitative test (it was the DNA version) on day 15,5 after the incident. The result came back today as negative. 24 hours after giving my blood to the blood bank for the test, I started having symptoms such as sore throat and enlarged shotty lymph nodes in my groin area. My doctor diagnosed me with upper respiratory tract infection and I now am taking antibiotics for. He wasn’t too well informed on the testing about my question and that is why I come here for your thoughts as experts in the field. Is it possible that I could be seroncoverting right now and the DNA PCR test missed it as it was negative? My personal thoughts are if I was seroconverting or started just 24 hours after I gave blood for the 15,5 day DNA PCR test, it should have picked up as positive right? What are your thoughts? Just to confirm again, I’m still on PEP. Thanks you doctors kindly.

    • If you are having symptoms due to ARS then presumably your test would be able to detect HIV. But as a general guide I do not really recommend PCR testing while a patient is on PEP, as you are essentially taking antivirals which will suppress viral load. It is a better indication if you do a 4th gen combo Ag/Ab test – these will be positive if symptoms are due to HIV. In any case, I do not think you are seroconverting. A recent study showed only 1 PEP failure out of close to 3700 cases.

  9. Hi Dr. I just read the comment you left to the previous individual and you said that he needed a test 3 months post PEP is it it 3 months post exposure or 3 months post PEP?

    • Different countries/organizations have different guidelines. I am happy with my patients repeating the test at 3 months post-exposure.

  10. Herman

    hi doc
    am a new graduate physician assistant but blood splashed in my eye when I was suturing an accident case,a few minutes the nurse wiped me of with an antiseptic and tested the guy was positive but (he didn’t know) .actually after around 30minutes I ran water in my eye and began PEP after 5hours. on my 14th day I did determine alere negative statpak repeatedly reactive a few days later did uni-gold negative but still stat pak reactive. And still on the same day (14th day taking pep) i sent my blood for pcr though am waiting for the results. please some word am worried

    • Are all 3 tests you are taking antibody-only? If so, they would not be a very good indication of your status given the early window period. Although a PCR test is a good indication now, there is some data to show reduction in sensitivity when you are on PEP (as they are antivirals and will suppress viral load). Best thing is to complete your PEP and do a 4th generation Ag/Ab combo test thereafter, with a repeat test at 3 months for completion.

  11. Martin90

    hi there docs

    i have a question for pep. i started it 60 hours post exposure with viraday. stupidly my exposure was unprotected receptive anal intrcourse with a recently infected hiv poz prostitute who is not taking medications.

    what is the likelihood of it working???
    have you seen ANY pep failures between 48 to 72 hours???
    is viraday a good pep regiman???

    I am losing my mind with worry. pls advice!! Tnx

    • Viraday is fine for PEP. I have not personally had any PEP failures if taken properly and with no further risky exposure while on the medication. PEP will essentially reduce your risk of HIV transmission by up to 50x.

      • Martin90

        Tnx you Doc. Just one question, even if I started it at 60 hours??? Would you consider this late???

  12. Gopal62

    Dear Sir,

    Thanking you for doing great job here. Please go through the sequences I have been through:

    I m 27 years male, Heterosexual
    Exposure: Condom breakage, Single 3-4 minutes exposure CSW, noticed after ejaculation.

    PEP: Luckily started taking TDF+3TC+ LPV/r within 4 hours of exposure. Complete adherence up to 28 days strictly.

    Side effect: felt fatigue moderate and some time loss of appetite.

    Physical changes: 3 kg weight loss, on and off one or two rashes sometimes, running nose 4 days. After PEP. No fever.
    Emotional changes: so much stressed and anxiety, sometimes suicidal ideation.

    Tests: 1) Baseline:Rapid HIV 1&2 negative, determine negative, Tpha negative, VDRL negative.
    2)5 week post exposure, 1 week post PEP:Rapid HIV 1&2 negative, determine negative I think Rapid is tridot kit.
    3) 10 week post exposure, 6 weeks post PEP : Rapid HIV 1&2 negative , determine negative, same test as previous.
    4) 12 week post exposure, 8 weeks post PEP:
    Fourth generation Elisa, HIV 1& 2 Ag / Ab screening test negative.

    I m regretting that I should have done previous tests with fourth generation on first week and six weeks post PEP rather than doing now on 12 weeks post exposure. I have searched a lot of things and cannot find if 4th generation test is same effective doing on 12 weeks as immediately after PEP.

    Please help me doctor with the query. Had followed all your recommendations for testing and PEP but thought all the testing I was doing latest fourth generation previously.
    Best blog for People with PEP at present. I want to move on thinking it’s conclusive now. Your single words would be decision for me.

    Thank You.

    • You do not have HIV, your tests are conclusive at this point. You can move on with your life.

      • Gopal62

        Much appreciated with prompt reply. Certainly I will move on. Just only a query .Is doing fourth generation Elisa effective 12 weeks post exposure, 8 weeks post PEP rather than doing previously on a week or 6 week post PEP.

        • 12 weeks post-exposure is fine.

          • Gopal 62

            Dear Sir,

            On my 4th generation Bio Rad Genscreen a ultra Ag-Ab on 8 week post exposure,
            OD value: 0.0620
            Ratio: 0.2490 but result was negative. Is it close to cut off value?? Will it reach cut off value with time. I was on PEP after vaginal exposure within 4 hours. Truvada and kaletra. Also lowest OD value tested today was 0.470 and ratio: 0.1888.
            Mine was near highest among all.
            Do PEP effect OD to reach Cut Off????

            From now on never disturb ???

            Thank you.

          • Your test is negative. We do not look at the level of the value. It is essentially conclusive at this point, but we still recommend a repeat test at 3 months post-exposure as per PEP guidelines.

  13. sandep

    Dear Dr.,
    i want to know that after insertive anal exposure i take pcr rna and elisa test at 17 th day after pep completed. and i also inform you that i take pep at 96 hours can you see any case which can turn positive after this test my both test are negative. and what are the chances of me in safe side please comment

    • Your tests are essentially conclusive, you do not have HIV. A repeat test at 3 months is still recommended post-PEP as a largely precautionary measure. PEP studies have only shown significant efficacy up to 72 hours post-exposure. So it is likely you would not have been infected even if you did not take the PEP.

      • sandeep

        Thanks Dr. Jonathan
        sorry doctor but after exosure i know that he was HIV positive. and i take PCR RNA for HiV 1
        please comment can we take elisa test at 28 th day after completed pep. i taken elisa test 4 the generation ?

        please comment i reply because monday is my 28 th day after completed pep.I listen that HIV2 is less reactive.
        and if i take PCR RNA for HIV at 28 th day after completed PEP it may be conclusive.
        because i want to clear and move in my life .
        Thanks

        • I would recommend the 4th generation combo test once you complete your PEP, and a repeat test (can be 3rd generation) 3 months post-exposure to complete testing.

          • kkkkkk

            HI, Dr. I really appreciate you for your this work you are really great.
            After insertive anal exposure with HIV + Person. I take duo test at 37 day after PEP and 72 day after exposure all are negative. I read US CDC PEP of guidelines 2016 in which he consider conclusive test at 3 month after exposure if person is not expose to Hepatits C. I check my hepatitus B & C at approx 49 day they are negative I know they are conclusive after 3 month. I read also he suggested regimen which cannot i take. i take different regimen it is
            1. Tenofovir Disoproxil Fumerate and Emtricitabine Tablet
            2. Lopinavire and Rionavir Tablets
            at near 95 hours after exposure.
            I know i take late it may be work or not

            AT last I know only one thing can i consider my test conclusive after 12 week exposure if iam not exposure to hepatitus C or 90 day after exposure or 90 day after PEP.

            Sorry for asking many question
            Please reply I wait
            Please suggest

          • I believe your tests are conclusive and you do not require any further testing.

  14. TuckerD55

    Hi Dr. Tan & Partners

    I had an exposure via receptive anal sex 12 days ago and have begun taking Atripla PEP after +-55 hours. I have three questions for you doctors.

    1) I’ve read your posts that it’s not too late and still efficient but from previous patients, have any taken PEP at this time and ended up seroconverting?

    2) What are the chances that it will work? Out of 1 to 10 with 10 being 100%?

    3) I plan to take a DNA PCR at 16 days post exposure although will still be on the Atripla PEP (I will be 15 tablets in). I have read that the RNA PCR is not recommended as it’s a viral load test however with the DNA will it give me a good indication of my status as it will look at the actual DNA in my blood?

    Please could you give me your professional outlook on this. Thank you sirs.

    • Hi, I personally have not encountered any PEP failures if taken properly. The chances of PEP failure are much less than 1/10 if taken properly and there are no further high risk exposures in between – this is when used for a known HIV+ exposure. There is no real need to do the DNA or RNA test midway through your PEP in my professional opinion. Just complete your PEP regimen and get tested with a 4th gen Ag/Ab combo test thereafter. You will be fine.

      • TuckerD55

        Thank you for the speedy reply Dr. Jonathan. Your response has lifted a lot of the worry I have which I say thank you for. I was however not clear in my first message to have outlined that the exposure was in fact with a HIV+ person who did not know that they were HIV+ so an extremely large viral load is expected.

        Three final questions which I would extremely appreciate your response – please could you answer them, please:

        1) With the fact that there are no further risky acts after administering the PEP. When you say you have not seen any PEP failures when taken properly, do you mean with good adherence or taken before the 72 hours cut off time limit? I ask as I am worried that +-55 hours is too late to have caught it.

        2) About that DNA PCR, if I were to take it at Day 16, in terms of a percentage how accurate would it be in your professsional opinion?

        3) When I take the 4th Generation DUO test at Day 31 which is the day after I complete the Atripla PEP course (30 tablets), how accurate will be the result?

        Thank you Dr!!!

        • Taking PEP properly means a) starting within 72 hours, and b) not missing doses for the entire course. There is some data to suggest DNA PCR may not be as accurate when a person is on PEP as essentially they would be taking antivirals targeted at reducing viral load. It will probably serve as a good indication, but it is not conclusive. If you take a 4th gen duo test after PEP, you result will be essentially conclusive. We would then recommend a repeat test at 3 months post-exposure largely out of precaution. There have been no validated cases of a negative 4th gen test post-PEP turning positive 3 months later.

          • TuckerD55

            Thank you again for the fast reply. Really from the bottom of my heart, thank you. You have offered your fast and knowledgeable advice without hestitation which impacts people’s lives in the most comforting way possible, case and point, yours truly.

            I will come back to this forum should I have any queries before the time PEP is over (I am however hoping this is not the case) although I will undoubtedly come back to tell you when I have tested with the DUO after PEP.

            All the best Dr!!
            May the force be with you.

  15. kuldeep

    Sorry Dr. But I cannot understand in this thread your reply for alper is that his result u take conclusive but in my case u say it’s good indication . He take pcr rna on 7 day after pep and I take pcr 17 day after pep and duo test I puzzle and I read pcr rna after 15 days 100% conclusive
    Sorry for this type of questions please reply I know my case is more risky because i expose with transgender but testing is not effect this situation they give only results.

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