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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

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We are now open on weekends.Find out more about Anonymous HIV testing at our clinics.Find out more about Anonymous Rapid HIV Combo tests at our clinics.More on HIV symptoms.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.Click Here for Contact Details, Address and Opening Times.

Related Articles:More on HIV SymptomsSTD General InfoHIV PEP Treatment at our ClinicHIV CMIA Test AccuracyHIV ELISA Test and HIV ECLIA Test

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. Please answer my question because I am so nervous. Is my 2 week post pep 4th gen Abbott test accurate?

  2. Hello Dr,please answer my question as I am very worried. 2 weeks after pep, my doctor did a 4th generation Abbott HIV test, and it came out negative. Is this conclusive and should i be concerned? Thank you so much.

  3. Hello doctors, I may have been exposed 8 weeks ago through protected receptive anal and mutual unprotected oral sex with another man of unknown status. Approximately 48 hours after, I initiated PEP.2 weeks after pep, my doc placed a 4th gen abbott hiv test. The result was nonreactive/negative. Is this a good indicator and onclusive?

  4. Hi doc,

    Sorry to disturb, had sex with CSW condom broke, we both tested HIV (-ve). I was on PEP for 28 days and tested with 4th gen combo test immediately after. My result was (-ve) are the results conclusive. Please reply. very worried


  5. Hello Doctor,
    I want to know about the combo test, when to take it for sure and is it 100% conclusive and don’t need to text for another 3 and 6 month. thank you.

  6. Hi Doctor
    I had a rapid hiv test by finger prick after the exposure of 28 days and the result was negative (anonymous test at other clinic)
    Am kind of worried still as I heard from the doctor that the result was not conclusive as the antibodies might be found within 3 months.
    Which puzzle me why it is conclusive at ur clinic after 28 days of exposure?
    Please let me know if the result is conclusive or should i test after 3 months of exposure pls ?
    Thanks a lot

  7. Doctor, I asked you a question regarding my post pep test reliability. After a vaginal exposure with a CSW of unknown status ( suspected condom failure). I was prescribed Travuda only Pep. I have had 4,6,8 and 12 weeks POST EXPOSURE, HIV test reported Negative. All 4th generation, lab based tests.
    On 16th Week post exposure I developed a flu like illness, cough,cold. Does it have to do anything with my previous exposure. Or my tests are reliable, I should not worry??
    Do I need anymore testing??
    Please Reply sir!! My Doctor here said I dont need anymore testing.
    I need your opinion.
    Thank you very much.

  8. hi sir,

    I had unprotected oral sex and protected vaginal sex both for 1 minute… I took PEP on the 4th day

    30 days post exposure I went for Alere determine ag/ab 4th generation test (AIDS foundation) and came back negative..

    however, it still shy of 2 days of PEP dose to finish… is the negative result 30 days post exposure and 2 days shy of PEP completion a conclusive result?

  9. Hi sir I’m have HIV pcr DNA qualitative test ofter 28day result noon reactivate and common HIV test offer 4,6,8mnths result negative and ofter 9months HIV pcr DNA qualitative test result noon reactive and ofter12 months common HIV test result noon reactive but I have urine infection sir plz help sir I’m safe or not safe

  10. Hi Dr Tan, I’m curious. When you say the 4 week test immediately after pep is very indicative, are you referring to a duo test or to the Determine rapid test? Thanks

    • Dr Justin Sim

      This is the duo test.

      • Hi doctor,
        Would a duo rapid test done at 6 weeks post exposure (2 weeks after completion of pep) be indicative?

        • Dr Justin Sim

          Yes it is a good indicator but post PEP you need to do an antibody test at 2 months to be sure.

    • I had protected sex with a HIV positive lady. I usually bleed after I brush but she said she doesn’t bleed through her mouth; I also fingered her. Am I at any risk? She noticed her status 11 days after we had sex subsequently I was placed on PEP. 6 weeks after; at the completion of the PEP, I tested negative to rapid test and was told to come back at three months time. I am worried because here in Africa only rapid test is available. can rapid test be conclusive on 8 weeks after exposure; I am depressed and emotionally down. 5 days from now will make it 8 weeks.

      • Dr Justin Sim

        Ideally you should repeat a rapid test 3 months after exposure to be sure. Your results are reassuring and your risk is low with protection but repeat once more for peace of mind.

  11. Hi,
    Thanks for clearing doubts about HIV,
    I have one dout , I took pep with in 12 hrs after my condem broken duringnsexnwith a call girl.
    My base line test in negative ,
    My 3 month and 6 month hiv test also hiv negative .

    My question is , is that result conclucive and no need to worry about hiv.?
    Any possibility to occure positive hiv result after 6 month …
    Need ur urgent clarification , pls support .

    • Even very conservative guidelines say that a HIV test at 6 months post exposure with PEP is conclusive.


  13. Good morning doctor,
    i have done hiv dna/pcr and antibody test at 12week,HABg n HCV antibody,all are negative,could this be conclusive?

    then what other test am expected to carry out.because i still have mild headache and mouth thrust.

    my doctor says nothing is wrong with me but am not feeling ok though am on ciprofloxacine 500mg bd

    • Yes they are. I do not think your symptoms have got anything to do with HIV. If you are really concerned, you may want to get yourself checked for other STDs as well.


  15. Good Day doctor

    I have posted a question on the 23rd but I wasn’t replied, please assist me.

  16. actually it was 3 months and a week

  17. Actually 3 months and a week

  18. Hi, i had a negative 4th gen hiv duo teat 9 weeks after pep(30 days) is it reliable? the problem is that i had many symptoms and my blood report was was not normal. is it possible to have hiv symptoms for 2 months and still test negative? my doc says i am ok but i am stressed.

    • Dr Justin Sim

      It is a good result but you should test at 3 months after exposure if you have taken PEP. Abnormal blood results this early are not to do with HIV.

      • 9 weeks after pep is 3 months after exposure,, is it then conclusive? i had other symptoms witch started 2 months before last test. is it possible to have symptoms of hiv witch start 2 months before last test and still test negative if it is due to hiv?


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