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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.

Click here for Info on STD Symptoms in Men
Click here for Info on STD Symptoms in Women
Click here for Info on HPV Testing in Men
Click here to see the full range of our HIV/STD Services



Need more advice?

Come down to Our Clinics for a discussion with Our Doctors, or call our clinics for more information:

1.) Robertson Walk  (+65 6238 7810)

2.) Bencoolen Street (+65 6884 4119)

3.) Novena Medical Centre (+65 6397 2095)

4.) Scotts Medical Centre (+65 6694 2348)

5.) Somerset – Orchard Building (+65 6262 0762)

6.) Katong – East Coast Road (+65 6635 2551)

Where to find us – here

Selected clinics are open on Saturday and Sunday.

Doctor’s Schedule here

Email: [email protected]

All Our Doctors are Fully Certified and Trained to conduct specialised HIV Testing.

For lady patients who prefer female doctors, we have professional certified female Doctors to attend to your medical needs.


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More on HIV symptoms.

If you have any questions, visit our free online forum on sexual health, HIV and STDs.

If you need a HIV test visit Our Clinics anytime during our opening hours. You do not need an appointment.

Find out more about Anonymous HIV testing at our clinics.

Can’t wait for 3 months to find out? Find out more about Anonymous Rapid HIV Combo test at our clinics.


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.

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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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All prices quoted below excludes prevailing GST


Consultation STD Consultation – $60.00

Anonymous HIV Rapid Test only $20.00
(not inclusive of test)

STD screening
Standard HIV, Syphilis, Hepatitis B/C, Herpes Simplex Virus Type I and II $ 200.00
Urine – Chlamydia and Gonorrhoea PCR, Monilia, Trichomonas, NSU, Mycoplasma, Ureaplasma, Urine Culture, Candida $ 280.00
Urethritis and Vaginitis
Vaginal Swab – Chlamydia and Gonorrhoea PCR, Monilia, Trichomonas PCR, Gardnerella PCR, Candida PCR, Group B StrepNSU, Mycoplasma, Ureaplasma, Direct Microscopy, Candida, Vaginal swab culture $ 345.00
Comprehensive (Male) Blood – Syphilis, Hepatitis B/C, Herpes Simplex Virus Type I and IIUrine – Chlamydia and Gonorrhoea PCR, Monilia, Trichomonas, NSU, Mycoplasma, Ureaplasma, Urine Culture, Candida $ 390.00
Comprehensive (Female) Blood – Syphilis, Hepatitis B/C, Herpes Simplex Virus Type I and IIVaginal Swab – Chlamydia and Gonorrhoea PCR, Monilia, Trichomonas PCR, Gardnerella PCR, Candida PCR, Group B StrepNSU, Mycoplasma, Ureaplasma, Direct Microscopy, Candida, Vaginal swab culture $ 525.00
Individual STD Tests
Determine Syphilis test Rapid Syphilis Test $ 50.00
Determine Hepatitis B Test Rapid Hepatitis B Test $ 50.00
Herpes Simplex Virus PCR Herpes Simplex Virus Polymerase Chain Reaction (PCR) Test $ 190.00
Chlamydia and Gonoccocal PCR Chlamydia and Gonorrhea
Herpes Simplex Virus Type I IgG Antibody Herpes Type 1 $ 40.00
Herpes Simplex Virus Type II IgG Antibody Herpes Type 2 $ 40.00
Non-Specific Urethritis (NSU) Culture Mycoplasma, Ureaplasma $ 118.00
HIV test
HIV RNA/DNA Polymerase Chain Reaction (PCR) Test $600
Add $100 for expedited results
Rapid Fingerprick Blood HIV-1/2 P24 Antigen/Antibody Combo (HIV Duo Test) (4th generation!) $ 150.00
Rapid Oral Saliva HIV-1/2 Antibody Test (Oraquick) $ 50.00
Rapid Fingerprick Blood HIV-1/2 Antibody Test (Determine) $ 50.00
PEP $2000 – $2200


  1. Please help

    I’m a male who had sex with a sex worker in the dominican republic 26 days ago. I went on pep (truvada and isentress) 68 hours after the exposure. Yesterday, I started to get a slight fever and had a sore throat. Today I went to the emergency room to get the rapid fourth generation hiv1, hiv2, and p24 antigen blood test. The results were negative. This is day 23 of Pep. I have 5 days left. Is this test conclusive?

    • Dr. Julian Ng


      You are still within the window period of the HIV test and thus the result is NOT conclusive. You will need to repeat it after 28 days.

  2. newyorker416

    Dear Doctors,

    Thank you so much for a wonderful informative website, it has helped keep my sanity in the past month. In early February I had a possible exposure (unprotected anal) with a man of unknown status. I started PEP less that 48 hours later. During my final week of PEP I started to get severe muscle aches, and joint pain. And a sore throat that is still here today. Severe headaches as well, Also lots of stomach issues. On March 12th I took my HIV test at the top hospital in NYC (also where pep was prescribed) and yesterday I got the negative result. It was the 4th gen AB/AG Lab blood draw test, not finger stick. I’m worried that this could possibly be a false negative because of my symptoms. My doctor said not to worry and that this is basically 100% conclusive. I started prep now but I’m still very anxious.
    I’m hoping my symptoms are just from the anxiety and not ARS. I spent the month in severe anxiety.

    Do you think I can breathe a sigh of relief and stop worrying? Is this test result based on the type of test accurate at 5 weeks post exposure even when taking pep? Thanks in advance for your answer.

    • Dr. Julian Ng


      I would agree that your result is conclusive. Your symptoms may or may not be HIV related. Please visit your doctor for further evaluation.

      • newyorker416

        But how could they be hiv related if my test was negative?

        • Dr. Julian Ng


          Assuming that the HIV test you did on 12th March was after 28 days post-exposure and it is negative, it is likely that your symptoms are not related to HIV. However, you should still seek further evaluation for your symptoms as there could be other medical conditions that can cause your symptoms.

  3. Doctor,
    I am on Prep (TenvirEM) for the last 60 days.

    I am planning to stop Prep.
    But recently 3 days back I had Unprotected sex with a Sex worker.

    So to stop PREP how long I should take Prep after Unprotected sex ?

    (On a very before day of Unprotected sex I missed I dose of Prep. But apart from that all 60 days I took Prep)

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