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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.

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, What are the chances of testing positive after a 81 days post exposure prophylaxis rapid antibody alere determine hiv 1 / 2 negative? Is the test reliable only at 3 months or 6 months? Thank you for replying. …

  2. Hi Dr, What are the chances of testing positive after a 81 days post exposure prophylaxis rapid antibody alere determine hiv 1 / 2 negative? Is the test reliable only at 3 months or 6 months? Thank you for replying. …

  3. madman

    First of all thanks for your kindly help to people who under big stress and tension.
    My question is,
    1) the combo Ag/ab test after exposure 102 days and after last dose pep 72 days is negative. Is this accurate or do I need another test?
    2) if you were in my place do you start ur girl friend without condom sex or waiting more months?

    • 1) It is accurate. You don’t need another test.
      2) This should be at your discretion. Condoms protect you from other STDs as well, therefore it is always advisable to use a condom.

  4. worried

    Sirvno reply from you yet…

  5. worried

    Hello dr tan
    I am little worried as i have few unanswered question hope you can answer my querys
    I was on truvada alone as pep for 30 days after my exposure which was a condom break while trying anal with a syrian prostitute of unknown hiv status though i could not manage to penetrate fully it was a very quick say almost 10 -15 seconds without any blood and ejaculation ..
    I got tested on fowwing intervals
    1. Antibody test on 7 days after exposure
    Result —Negative
    2. 4th gen combo test ab / ag 14 days after exposure
    Result —- non reactive ( .13)
    3. 4th gen combo ab/ag test 28 days after post exposure
    Result —- non reactive (.11)
    4. 4 th gen combo ab/ag test 6 weeks after exposure ( 2 weeks post pep )
    Result —– non reactive (.09)
    5. 4 gen combo ab/ag test 14 weeks post exposure ( 8 weeks post pep )
    Result —- non reactive (.11)

    Dr i want to know that do i still have chance of getting hiv in future due to this single short exposure as i had no other exposure since then.
    Should i get tested again.
    Why did the value of my combo test done at 14 week came back to 0.11 after coming donwn to 0.09 at 6 week is it somthing to worry about
    I want to plan my family so can i have condom less sex with my wife …?
    Or should i wait feww more months to be sure ..
    If i need to get any future testing then which test should i opt for
    I have not had sex till date so advice me as i can go ahead with my sexual life

    Can i continue my life without fear
    Can truvada affect my test reports …?

    Awaiting your precious reply ..

    • worried

      Sir i am eagerly waiting for your reply..

    • In my opinion your tests are already conclusive. You do not have HIV.

      • Thomas

        I recently had a brief (about 4-5 minutes) vaginal encounter with a recently infected lady. At first we did not use condoms (about 4-5 minutes) but we later used it. I managed to be on PEP within 18 hours after the encounter. Its been 8 weeks i.e. 28 days PEP and weeks after completion of PEP. I had taken rapid tests which indicates that I am HIV negative and my Dr is 95 percent certain that i am not HIV positive. In addition is that I am also circumcised. So my question to you is, should i believe my Dr that I am HIV negative or should I assume that I might be HIV positive as well?. Please help I am so stressed.

        • I am in no position to comment whether you should believe your doctor or not.
          It depends on which rapid test you did. If it is a 4th generation combo test, then yes it is conclusive. If it is oraquick or Alere Determine 1/2, then it is not.
          If you are worried, you should get yourself tested again at 3 and 6 months post exposure.

          • Thomas

            Thank you very much for the reply DR. The test I did was HIV (1&2) POCT approved by WHO. I did another test (HIV (1&2) POCT) on monday and it came back negative i.e. 32 days post PEP.I hope this helps. Eagerly waiting for your response. Regards

          • If you are worried, you can get yourself tested again at 3 months.

          • Thomas

            Helow again DR. What realy needed your opinion if its conclusive enough or i should also do follow up tests?

      • Thomas

        Hi Dr Tan. I recently had a brief (about 4-5 minutes) vaginal encounter with a recently infected lady. At first we did not use condoms (about 4-5 minutes) but we later used it. I managed to be on PEP within 18 hours after the encounter. Its been 8 weeks i.e. 28 days PEP and 4 weeks after completion of PEP. I had taken rapid tests which indicates that I am HIV negative and my Dr is 95 percent certain that i am not HIV positive. In addition is that I am also circumcised. So my question to you is, should i believe my Dr that I am HIV negative or should I assume that I might be HIV positive as well?. Please help I am so stressed.

      • Thomas

        Hi Dr. I recently had a brief (about 4-5 minutes) vaginal encounter with a recently infected lady. At first we did not use condoms (about 4-5 minutes) but we later used it. I managed to be on PEP within 18 hours after the encounter. Its been 8 weeks i.e. 28 days PEP and weeks after completion of PEP. I had taken rapid tests which indicates that I am HIV negative and my Dr is 95 percent certain that i am not HIV positive. In addition is that I am also circumcised. So my question to you is, should i believe my Dr that I am HIV negative or should I assume that I might be HIV positive as well?. How are rapid test hiv1/2 reliable at 28 days post pep?.

        Please help I am so stressed.

  6. Hi Dr. Tan, I started PEP late into the 72 hour mark due to difficulty with getting the medication and the insurance company. I did take one dose of Truvada and 1 of Isentress but not the second within the 72 hour mark since Isentress is every 12 hours. I am worried that because I couldn’t get all three doses in before the 72 hour mark, it will not be as effective . Thank you,

    • PEP is effective within 72 hours. You should get yourself tested at 4-6 weeks.

      • Dr. Liong, Thank you for such a fast response, I have a follow up question. I have had no side effects to either Truvada or Isentress while I normally believe that’s a great thing. Should I be concerned that the PEP treatment is not working? I have been reading online personal experiences from the treatment and have yet to hear of someone without any side effects. Thank you again.

        • You should not be worried that PEP is not working even though you don’t suffer from any side effects. Having side effects has nothing to do with the effectiveness.

          • Dr. Liong, Good morning, thank you again for such a fast response. My last follow up question, my primary physician has scheduled me to be tested 30 days after my last dose of the medications, the 3 month & 6 month mark. My question is, if I take an Oraquick home test a week after my last dose would it be considered accurate and conclusive? Thank you..

          • The answer is no. Oraquick is only conclusive after 12 weeks post exposure.

  7. Hi Dr.

    1. Based on your experience, how accurate do you think taking the Clearview Rapid test 9 days after finishing PEP is? I plan on taking another test at 12 weeks.

    2. How likely am I to transmit HIV (if I contracted it) while on PEP? We were both drunk and he penetrated me via anal briefly for less than a minute. I was on my 23rd day of PEP (Truvada + Isentress) when it occurred (April 5th). Yesterday, he came down with a 101F and flu-like symptoms. I am worried sick that I might have infected him.

    Thank you for all of your help

  8. worried

    How reliable is a rapid antibody hiv 1/2 determine at 70 days post exposure prophylaxis?
    Exposure having vaginal sex with an expired condom without being ruptured for 2-3 minutes. Started on PEP 52hrs after exposure and tested 70 days post exposure prophylaxis with alere determine hiv 1/2 antibody. How reliable is that test?

    • Very indicative but not 100%.

      • worried

        Thank you Dr Tan for your quick respond.Very much appreciate your good work. Does that mean I should get another alere determine hiv 1/2 antibody test 90 days post exposure prophylaxis to consider it conclusive or what is your recommendation?

  9. Hello Dr
    I asked a question before but i confused so ask again. My previous question is i took Truvada for 6 days and after i stopped to take a Truvada and i asked will take a only 6 days Truvada affect to hiv test results and you answered it don’t affect to test results but when i searched the internet world health organization (who) don’t publish to article for take 6 days Truvada will affect or don’t affect to hiv test results. So you inform to don’t affect to test results but i’m not sure so i want to take a confirmation for don’t affect to hiv test results so i ask again. Are your comment is conclusive? Will i be sure that don’t affect to hiv test results? What is your opinion for 4th gen hiv test? When will i have a 4 th gen test for conclusive results ?
    Thanks for your comment

  10. PEP Qns

    Hi Doctors,

    I’ve had a protected vaginal sex and non-protected oral sex with an escort recently and went to see a doctor at one of your clinics. Given that it was a sexual encounter with a CSW, the doctor who attended said it was a moderate risk event and said it was my decision whether to take PEP (within 45hrs of exposure). Eventually I decided to go ahead with PEP, however, I’ve a few questions that I hope you can answer as it won’t be in a couple of weeks before the combo test (recommended by doc instead of HIV RNA test):

    1) If you have to access my chances of contracting HIV based on the info above, what would be the figure that you would quote?

    2) If I’ve to take a test before 28 days (around 23 days post potential exposure) for a reason, how accurate do you think the test would be?

    3) Since I am currently on PEP, would it affect my test results at 23 and 30 days (intent to retest at 30 days since my first test has to be around 23 days)in your opinion?

    4) If I test negative at 23 or 30 days, would it still be necessary to have protected sex with my partner? If so, how long before this is no longer required that will not put my partner at risk?

    5) If the tests are negative, does that mean I was not infected or does that mean the infection was aborted? If it is the latter, is there any chance the virus can be “reactivated” in the future or will it be flushed out of the blood eventually?

    Apologies for the many questions as this fear is eating into me and I read information here and elsewhere that are at times conflicting. This is a moment of folly that I’ll never repeat again! Thanks again in advance for your help doctors.

    • Dr Justin Sim

      1) This is difficult to put an accurate number to because you had different exposures in the same sitting. But vaginal sex produces approximately 1/2000 risk for contracting HIV – oral sex is very very low risk.
      2) Doing a test before the end of your PEP is not advisable because the test will not be conclusive. We can’t put accurate numbers to it because the potential range is quite wide (anything from 50-80%). I would recommend getting tested after the end of your PEP.
      3) Yes the PEP will affect the test results if you take the test early.
      4) You will still need protection until after your test at 30 days. If the 30 day test is negative then you still need to do a final follow up test (call it a confirmatory test) 2 months later to be absolutely sure.
      5) It could be both – it would be impossible to tell. If the virus has been eliminated then it will not reactivate. However, if the PEP was improperly taken or you fall into the 5% that may not respond to PEP then the virus will not be eliminated and could reactivate.

      • PEP Qns

        Hi Dr,

        Thanks for the reply. Sorry, I’ve a couple of follow-on questions:

        Regarding 1), is that the probability for protected or unprotected vaginal sex?

        Regarding 5), am I right to say that you are saying that even if I test negative two months after PEP, it will still not be conclusive? Wouldnt the tests at 1 month or 3 months have shown the failure of PEP? If the tests cannot be conclusive at 3 months after exposure (even if it shows up as negative), does it mean that I cannot be certain ever that I am HIV -ve even if I never engage in casual sex encounters again? I need to know if there is a point that I can move on with my life plans.

        Sorry for the multiple questions, really appreciate your advice as I am quite confused and scared. Thanks.

      • PEP Qns


        I posted a follow-up question that was not published but I really need a medical opinion on it:

        W.R.T the answer to Qn.5, could I check if the 3 months post exposure combo is considered as conclusive as HIV negative for life (assuming one does not engage in risky sexual behavior in the future)? Is there a chance that (if one is infected) the virus will not be eliminated and reactivated in the future??

        Really need an answer doctors on this because I need to know if there is a point that I can take the test to be conclusive.

        • Dr Justin Sim

          Yes if you check with the combo at 3 months which is negative then you do not have HIV in your system and this would technically hold true for life as long as you do not risk any new exposure. There is a chance that it may not have been completely eliminated with PEP but that is a risk with all medicine – nothing can ever be 100% but PEP gives you the best chance to eliminate the virus at the early stage. The following combo test done at 3 months can pick up a reactivation if PEP has failed.

          The test is important – without it we would have no idea of your status which is why we may recommend tests further down the line if you are particularly anxious and wanted extra peace of mind.

  11. Dear Dr Tan,
    Hope your are doing well.
    I was under PEP treatment ( daily = Truvada + Scotrin ) for 30 days and after 3 days I did a test of Anti HIV 1 & 2 with also P24 Antigen test. The results is Negative.
    How accurante is this results just to have an Idea so I feel more reassured.
    For sure I will repeat this test at 3 months but just I want to know what the % that this Test reuslts I get it correct.
    Thank you a lot for your respons in advance

  12. Hi
    I took a PEP but it’s not correct i took only Truvada for 6 days but i gave up to Truvada at 6th days cause of side effects. I wonder is it possible to influance the test results for 4th gen P24 test and PCR test. I will think that have a 4th gen P24 antigen test and also PCR test but i don’t know to when will i have a test? Please advice which day have i P24 antigen test and PCR test? Thanks for your your comment.

    • Dr Justin Sim

      If you have only taken for 6 days then it is unlikely to affect the tests. Not enough of the medication will have entered your system to be effective. However, to be safe it is probably best to check with a 4th gen test at 4 weeks post exposure then a 3rd or 4th gen test at 12 weeks post exposure.

      • Hello Dr Justin Sim
        Thanks for your reply. Also i want to ask another questions. In Turkey some laboratuary said that at 14th day you will take a conclusive result (%99,88) which is test name is Vidas Hiv duo ultra. This test looks P24 antigen and antibody. What do you think about this test? If i have this test at 14th day will i have a conclusive result. Another question is what dou you think about PCR test this test looks a Hiv RNA and laboratuary said that after 11st day you will take a conclusive test. When will i have the PCR test for conclusive result. I’m worried the Hiv so i want to take a conclusive result as soon as possible. So please advice which test will i have for conclusive results in the earliest time.
        Thank for your help

  13. Loyaltee

    Hello Dr. Tan,

    From 3/1/15 – 3/20/15 I had 3 unprotected vaginal-penile exposures in which he ejaculated inside me. I performed oral 2x in which there was ejaculation 1x (I gargled with mouthwash immediately). I also received oral 1x. I found out that this person is HIV positive on 3/21/15 and has been for years. I tested negative on an INSTI HIV antibody test on 3/21/15 and began PEP (Combivir) the same day as my last exposure was the night before. I saw his most recent bloodwork which was done the end of Jan. His CD4 count was 240 and his viral load had “< 40…" and an "N" next to it. I am not quite sure If the number was his value or a reference and I don't know what the "N" stands for. He claims his doc told him he's undetectable. Since that test he has slept with multiple partners some of whom were positive which could have driven up his load although he claims to have used condoms. He had bloodwork done on 3/24/15 but viral load was not measured. His CD4 count was 430 which was up since the testing done in Jan. I did a Home Access HIV test on 4/1/15 (1 month after 1st exposure, day 11 of PEP) and it was negative. How reliable are the rresults of the 2 tests I took with all things considered? Thank you so much for your response.

    • I understand your concerns. Fortunately, your risk of HIV is low. First of all, getting HIV from penile-vaginal sex (even if unprotected) is relatively low at about 1% to 6%. Secondly, I assume your partner is on ART (and his viral load is undetectable) which drops the risk by another 87% to 90%. What I find strange is that you were given Combivir as PEP. Most guidelines do not recommend that anymore. Based on this I would say the chance you have HIV is very low. I would not put any credence on the tests that you have done because they were done too early.

  14. I had a occupational exposure. I began PEP within 4 hours on day 10 of PEP a new partner and I had sex. The condom broke. I continued with my PEP treatment but the Dr extended it by 14 days. I am now on the 20th day after finishing PEP. Today I was seen by a doctor because I had a 102 fever, swollen throat, and felt sick. I’ve had 2 4th generation tests, one at 3 weeks post exposure and one at 6 weeks both negative. Is the sickness today indicative of seroconversion and failed PEP treatment..The doctor completed a rapid INSTI test tonight on week 7 after the 2nd possible exposure and it was negative. Any help would be greatly appreciated. Thank you.

    • Dr Justin Sim

      Unlikely due to seroconversion – more likely due to a cold or flu virus. However, it is important that you still do one more HIV test 2 months after completing your PEP to be sure it is clear.

  15. Hello Dr. Tan,
    I started PEP medications at 67h post exposure. I tested today (Ag/Ac VIH Combo) at 26 days post-exposure (24 days taking PEP) and came out to be negative. Should I complete the 28-day course of PEP, or are the test results reliable enough to stop the medications? Just to avoid any more damage to the liver.
    I was prescribed with Atripla (Emtricitabine/tenofovir/efavirenz).

    Thank you in advance for your time

    • Dr Justin Sim

      Yes you must complete the course – that is very important. The tests at this stage should not be an indicator to stop medicine, it is actually quite the opposite. You will need testing after you finish PEP and 2 months after exposure to be sure. Remember that PEP supresses the virus to a low enough level for the body to eliminate it, which is why longer follow up may be needed.

  16. Hi doc,
    I took pep just for two days starting at 65 hr mark. I stopped pep after 2 days because of side effects. I came to your clinic at unity street for 4 gen test at 21 and 28 days post exposure. Both were negetive. Doctor said the result is conclusive. But i took pep though for very short time 2 days. Now it is over 6 week of exposure. What do u think about my result? Are they conclusive even after pep or should I get tested again. And also, what would be accuracy if I get tested now?

    • Dr Justin Sim

      Taking 2 days of PEP won’t effect the result. The 28 combo test will still be conclusive. However, if you are concerned then you may want another test to confirm.

  17. clinton

    I live in Africa in a high risk area of aids. I made a huge mistake after getting drunk and didn’t wear a condom with a women i just met. I started PEP within 14hrs and its now day 2.

    However, I have just managed to track down the women I slept with and had a blood test that goes straight to the lab and gives a result for HIV 1 & 2 within 30mins.

    Turns out she is negative, should I now stop the medication? Or is it possible she was in her window period and has the disease and still passed it on?

    Looking for advice in what you would do in this situation, and I will also be discussing it with my Dr in the next few days.

    Also the drugs I am taking are lopinavir/Ritoavir & Emtricitabine/Tenofovir and I read that these drugs can be fatal. That has me really panicking, does it happen fast or is only after exposure for a long time.

    You must understand that although i can/and will discuss this with my Dr, Africa sometimes doesn’t produce the best candidates to give advice.

    Thank you kindly

    • It is possible that she is within the window period. People who are within the window period are usually extremely contagious due to a high viral load. I personally will not ask my patients to stop their PEP because their partner tested negative just after the exposure. Saying those drugs can be fatal is being a bit dramatic. Just like any other drug, those drugs have their side effects. And although I agree the side effects can be rather bad, I have never seen them kill anyone. You must weigh up the pros and cons of treatment. The risk of the drug side effects versus the risk of being infected with HIV. This forum is only for sharing information and you should still defer to your doctor’s medical advice.

  18. Hello Doctor Tan,

    I took PEP and tested with ECLIA 3rd generation test or 4th generation test at week 14 post exposure(10 weeks post PEP). The same day I’ve also done Oraquick home test. They gave the same result. How accurate are my 2 testes? -Thank you very much doctor-

  19. Dr, I want to raise an interesting question. What is the possibility of acquiring a theoretical new strain of HIV through unprotected sex? Because HIV mutates much more than the human genome. I have no idea of how detecting a new strain works, i.e. when they detected HIV-2 for the first time, or the new strain of HIV in Cuba that causes AIDS more rapidly. But I suppose that it was not with the traditional tests. So if someone got infected with, let’s say, “HIV-3″ or “HIV-1 clade XYZ”, it would go undetected until 10 years pass and the person starts to show signs of AIDS. Is that right or not a possibility today?

    • Of course that is a possibility. In fact, prior to 1981, we did not even know of the existence of HIV. Some scientists believe HIV was around in humans since the 1800’s. SO effectively it went undetected for 100 years. This is how medicine evolves. We discover new diseases just like biologist discover new species. By then some people would have died of it. That’s sad but that’s how it is. If the scientist in 1981 did not publish the MMW Report on young homosexual men dying of PC Pneumonia, perhaps even until now we will not know of the existence of HIV. But why limit this theory of yours to HIV? Essentially, there can be a bacteria of virus that is killing people right now that we have yet to identify. That is also a possibility. So what can we do about it but remain vigilant, ensure good communication among doctors and scientists throughout the world and allow medical science to progress.

      • Oh, I see. I mainly limited this thought of mine because I’ve had unprotected sex twice in my life, so, you know, I would be a candidate for getting infected with an undetectable strain. And I’m a very curious person that likes to go deep into an issue.
        Having said that and confirming the possibility, do you know maybe if the current recombinant strain that they discovered in Cuba was detectable by the current tests? I tried to find scientific material on how they detect new strains, but all I find is mere scientific commenting over the fact itself.
        By the way, I think that the terrifying thought that an occult epidemic of an HIV-3 itself (instead of a new recombinant strain of 1&2) would be much more difficult to happen that way.
        Either way, I’m getting a CD4 test in 5 years lol

        • How they detect new strains is first people start getting very sick from HIV. When they finally realize it is HIV they sequence the genes and go “OMG! It’s a new strain!” Of course it is much more complex than that but in a nutshell that is what happens.

          • So if I’m concerned about it, getting a CD4 count regularly is the best thing I can do?

          • I don’t know about that. Your CD4 will naturally go up and down. You might just be causing yourself a lot of unnecessary worry.

  20. Paradigmshift

    Hello Dr. Tan,

    I want to know how accurate/reliable a 3rd generation antibody laboratory test is at 30 days post exposure (1 day shy of completing my entire 30 day PEP prescription)? My results were negative at 30 days(4 weeks), and this week marks the 12 week mark when I have to return for follow up testing. I am very nervous and have been for the last couple of months.

    I read your most recent reply to “BeachVolleyball” and although our questions are similar, that individual tested at 35 days. I just want to know your opinion on the reliability of a 30 day negative result.

    Thank you in advance for your time and information.

    • Your test this week at 12 weeks will be clear. I think the 3rd Gen ab test at 30 days post exposure even with PEP is very close to 100% accurate. You really need not be too concerned.

  21. BeachVolleyball

    Hi Dr. Tan,
    How reliable is a 3rd generation antibody rapid check test along with an Western Blot both done 35 days post exposure (5 days after end of PEP)? Results came back as Non-Reactive according to the nurse.
    I will take a 4th generation test at 12 weeks, but I’m so preoccupied with the possibility of seroconversion during that time.
    Thank you!

    • From my experience the 3rd Gen Antibody test at 35 days post exposure even after PEP is very close to 100% accurate. You really should not worry.


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