Dr. Tan and Partners is one of the few approved Anonymous HIV Testing Centres in Singapore. A detailed write up on our service is available here.

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HIV Window Period

Are your HIV tests accurate?

HIV testing may seem very complex.

This is greatly due to the testing ‘Window Period‘. That irksome time from when a person is infected to when tests can actually detect a HIV infection.

Click here to read about the Biology behind the Window Period

HIV Signs and Symptoms

The HIV Window Period and Test Accuracy

HIV PEP Post Exposure Prophylaxis

This has caused a lot of doubt and worry with regards to the accuracy of tests done.

You might even be wondering right now how accurate your tests are.

There is a lot of confusing information out there. Some people claiming a window period of 2 weeks some people even saying 10 years!

This is because HIV testing technology has developed significantly since HIV was discovered in the 1980’s.

So a lot of information out there is out-dated.

Also, not the same standard of tests are available everywhere. This has caused different governments and different health authorities to develop different testing guidelines. So the reason why the Window Period is different in Massachusetts is different from Singapore is not because humans in the US react differently to HIV compared to humans in Singapore. It is because of local guidelines.

So what exactly if the HIV Window Period?

It depends a lot on WHICH TEST was done.

The following graph was prepared based on the latest information on Testing for the Diagnosis of HIV Infection.

HIV Testing Window Period for various Tests

HIV Testing Window Period for various Tests








Some points to note:

1. If you are within the first 10 days of possible HIV infection (aka the Eclipse Period), don’t bother doing any tests. There are NO tests that are accurate.

NB: If you are within the first 3 days of possible HIV infection please see us about PEP.

HIV Prevention within 72 hours of exposure (PEP) – Click Here

2. At day 10, the HIV-1 RNA PCR can detect HIV Viruses in the blood.

Remember that the RNA PCR test has a high chance of giving a false positive result.

If the RNA PCR test gives a report of less than 5000 viral copies per ml, it is likely a false positive.

Click here for information on HIV RNA testing at our Clinics

Also, the viral load may drop to an undetectable level upon full sero-conversion.

This is because the body’s immune system may have suppressed the infection to a point where there is not enough HIV virus in the blood for the RNA PCR test to detect.

3. Between day 14 to day 20, the HIV P24 Antigen will start appearing in the blood. This can be detected with 4th Generation tests (aka Combo tests).

This is why, although the official recommended Window Period for the Combo Test is 28 days, we are very confident when a patient tests negative at 2 weeks.

Remember that the P24 Antigen level will peak at about day 28 and becomes undetectable at about 6 weeks from infection.

This does NOT mean the 4th Generation (Combo) test is inaccurate after 6 weeks because the Combo test also detects IgM and IgG Antibodies (See below).

Click here to learn more about the Combo Test at our Clinics

4. Between day 20 and day 23, the IgM Antibody starts to become detectable in the blood.

This is only detectable by 3rd and 4th Generation HIV tests.

This is the other reason why even though the 4th Generation (aka Combo) test is supposed to be conclusive at 28 days, at 3 weeks when a patient is negative, we tell him/her it is as good as conclusive.

5. Between day 28 and 48, the IgG Antibody starts to become detectable in the blood.

This is detectable by 1st, 2nd, 3rd and 4th Generation HIV tests.

This will remain detectable in the blood for as long as a person lives. Therefore, doing a Combo test not only detects HIV infections that occurred recently, it also detects infections from years ago.

Click here for HIV Testing FAQ

More things to note:

The recommended 1st line screening for HIV infection is the Combo test NOT the antibody test.

So when you go for a HIV screening test, you should be asking for a Combo test. Take note that in Singapore the Combo test costs more than an antibody test.

The essential thing to remember about HIV testing is to get the RIGHT test done at the RIGHT time.

Come see us for professional advice on which test you need to do.

Click here to see the full range of our HIV/STD Services

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

Your are welcome to visit Our Doctors at Our Clinics anytime during our opening hours.


Click Here for Contact Details, Address and Opening Times.
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Our Andrology and Infection Centre at Novena Medical Center is open.

Call us at 63972095 now to book your treatment.

Feel free to email your queries, feedback and suggestions on what other topics you want to see in the comments section below.

All prices quoted below excludes prevailing GST

We are Open on Saturdays and Sundays.

Click Here for Contact Details, Address and Opening Times.


We have 5 locations conveniently located at Robertson Walk, Bencoolen Street, Novena, Scotts (Pacific Plaza) and Somerset (H&M)

Robertson Walk          6238 7810   map

Bencoolen Street        6884 4119   map

Novena                           63972095   map

Scotts                              66942348   map

Somerset                       62620762   map

Email: [email protected]



If you have any questions, visit our free online forum on sexual health, HIV and STDs.More on HIV symptoms.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.We are now open on weekends.Related Articles:HIV CMIA Test AccuracyHIV ELISA and ECLIA testGetting HIV from Oral SexMore on HIV symptomsHow long can HIV live outside the body?Erectile DysfunctionPremature Ejaculation

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.

Find the profiles of our panel of doctors.

Consultation $20.00-80.00
Rapid test only $20.00
(not inclusive of test)
8am – 5pm $60.00
5pm – 9pm $80.00
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. Hello Dr., I tested negative using the 4th gen combo test on the 15th day of possible exposure, on the 24th day, on the 29th day and once again on day 45. I have had a persistent cough that won’t seem to go away, would you say my results are conclusive or should I test again? Thank you.

    • Your tests are conclusive, you do not have HIV and do not need further tests. Get your cough assessed at a doctor – there are a hundred other more likely causes of cough.

  2. Hi
    Had a possible exposure with a homosexual mail…got my PCR RNA done at 7th day which is negative… doctor has advised me to not do any futher check as he claims it to be conclusive…

    What do you suggest…

    • HIV PCR RNA is considered essentially conclusive at 10 days. It is not an official diagnostic test for HIV, so as such we would still recommend a 4th gen HIV combo test at 28 days.

      • I am worried now… I would get a test done… but what are chances that its positive after 28days

  3. Hi Doc
    I had a protected sex with an CSW, however during withdrawal the condom stayed inside her…Not sure what time it came off, she was on top of me rubbing.

    Am i at risk, have gor PCR RNA done at 10th day which is negative…

    • The initial exposure would pose a risk but your HIV RNA test is done and essentially conclusive, so there is nothing to worry about now. Make sure you check for other STDs as well such as chlamydia and gonorrhea, etc.

      • Thanks Doc, are you saying the risk is due to condom coming off.. When I checked with lady she said it only came off during withdrawal… is this much exposure sufficiant for having a risk.. are such encounters risky and what are my chances I have HIV… I head women to men is considored very low risk

  4. Hi Dr.,

    Basically, I had a casual encounter (mutual masturbation), he masturbated me and he masturbated himself and ejaculated on my chest/stomach. As far as I could remember I had no cuts on my body during those times. Three weeks after that encounter I had a sore throat which up until now is still present. I performed the following tests:

    4th gen (15 days after encounter) – Negative
    4th gen (33 days after encounter) – Negative
    3rd gen (57 days after encounter) – Negative
    3rd gen (75 days after encounter) – Negative

    Will this be considered conclusive?

  5. Dear Doctor,

    I did 4th generation HIV combo test on 75th day of possible exposure (protected with condom).

    Is it conclusive or I need further testing?

  6. Perhan Nugraha

    Dear Doctor.. have you ever seen/heard of a 4th generation negative hiv test at one month turning out to be positive after 3 months?

  7. Perhan Nugraha

    Doc, one question
    Have you ever seen/heard a negative hiv test with in 2 months turns out to be possitive later?

  8. kishore kumar

    Hi Doctor, I had exposed to gonorrhoea and chlamydia and got treated. i had tested for HIV and other SITs on 15th & 36 days of exposure. both tests came back all negative. But im suffering from chronic diarrhea, swollen lymphs and severe caugh. Am I still at the risk of HIV?

    • If the HIV test was a 4th generation combo (antigen and antibody) then it was conclusive. If not, you would need to repeat a test at 3 months (if using a 3rd gen test).

  9. HI Doctor,

    i did the hiv1/2 determine rapid test for antibodies last sunday. This was after 7 months exposure ( feb was time of exposure) . My results are non reactive. Are these conclusive or do i have to take the antigen combo test as well?

    Furthermore do these antibodies remain in our body forever? And also will the p24 test pick up infections that the antibody test could not?

    Thank you very much Doctor

  10. I had HIV-1/2 &P24 tests after 18 and 33 days of the exposure. Both are negative. Are these conclusive?

  11. Is hiv dna pcr qualitative test accurate after 57 days after exposure? Plz reply.

  12. Doctor, I had a 4th generation combo test 18 days after exposure, about 3 months back. The test came back negative, and I haven’t shown any symptoms of ARS. Do I need to retest now for a conclusive result?

    • Yes, we would recommend a repeat test for conclusive results. Up to 70% of people infected with HIV will have no ARS symptoms.

      • But based on point 3 as written above, it indicates that with 4th Gen combo test, you guys are very confident that if the patient is tested negative, he or she will be considered HIV negative. However, your reply seems to contradict what was written above

        • As it states, we are confident of the result but it is not officially conclusive until 28 days post exposure.

          • Well, if that’s that case, pertaining to point 4 whereby you guys indicated, quote “at 3 weeks when a patient is negative, we tell him/her it is as good as as conclusive”. This is also not official as it is less than 28 days exposure and doesn’t mean he/she has to take the test again to officially confirm his/her status. Not trying to prove any case here but since you guys allows comments/questions, I sincerely hope your reply can be more specific rather than generic.

            Understand anything written here may have legal obligations if things do not turn out as per said but I think most of the people here are concerned about their health and was hoping to have assurance in any form. Again I know they are responsible for involving in such activities but you guys are doctors and doctors are supposed to help physically and mentally.

            I’m someone who went through this and had several anxiety attacks because of this so I kind of empathise the people who are really worried and concerned

          • I tell my patients exactly what I have written here – if they have taken the test at 3 weeks, I say this is an extremely good indication but officially you would need a repeat at 28 days for 100% conclusive results. This is not being generic, but it is the nature of population-based probabilities. The virus does not choose a day for it to become detectable – the numbers are obtained from population-based studies, knowledge of viral replication, etc. We try to be as forthcoming and accurate as possible with current scientific knowledge.

          • Pertaining to your latest feedback, I’m fully aware and totally agree with you on, quote “if they have taken the test at 3 weeks, I say this is an extremely good indication..” and this is exactly what I’m hoping to hear from a doctor when i posted a question like what Sam did rather than just quote “yes, we would recommend a repeat test for conclusive results”

            In my humble opinion, the first sentence will be extremely helpful and will help to put the patient mind at ease, even only for awhile. Anyway, thank you for your advice and help..especially in this field because contracting HIV is really a big issue and turning point in life which I believe everyone here is hoping to avoid. You guys are heroes in my opinion

          • Dear Sr. Jonathan, good afternoon!

            as per you combo test is 100% conclusive after 28 days which now WHO & British guidelines are saying then why CDC & other major guidelines are not accepting this fact

          • If I worked at the CDC maybe I could tell you. Unfortunately, I do not. You will need to ask them about their guidelines.

  13. Hi,

    Lots of conflicting messages online,

    I am currently on PEP, and am due my 28 day post exposure test in 3 weeks time.

    Would a negative 4th generation test immediatly after PEP be encouraging in your opinion or does PEP delay possible infection as some people say?

    I notice on your site you believe that even on PEP 28 days 4th gen duo test is very encouraging?


    • Yes it is very indicative. There have been no cases of a negative test post-PEP becoming positive later on if the PEP was taken properly and there were no other high risk exposures in between.

  14. Is Malaysia using gen 4th for hiv test? I did the test about 23 days and negative result, how accurate the test? I online check with the lab already, they mention they using 4th gen. Is the 4th gen Malaysia and Singapore same?

    • I see no reason not to believe what the lab says. In any case, your result is not conclusive until at least 28 days post-exposure.

      • Not I dun wan to believe. Bcz from your website, you can give a conclusive result after 28days, thus, im thinking is it different test I’m taking.

        • Malaysia ask me take another test after 3 months and 6 months to conclude.

  15. Dear doctor,

    I had an unprotected anal sex with male (the highest risk category). I did the first test 41 days after the exposure and it came back negative. It was the 4th generation Ag/Ab Hiv test. In the lab where I did the test (I am from Serbia, South East Europe) they said that the window period for test which they use is between 6 and 8 weeks and they confirm that the test is the 4th generation.

    1. Do all test of the 4th generation have the same window period (28 days)?

    2. How conclusive is my result 41 days after the exposure?

    3. Could the fact that I did test one day before the six-week period affect my result?

    I am going to do test after 8 weeks but I feel very anxious about my further results.

    • Current 4th generation tests have a window period of 28 days. However, different countries may follow different guidelines, and it is best you heed the advice of your local healthcare professionals.

  16. sandeep

    Please advice me help me can I come in ur clnic I am really very depressed

  17. sandeep

    Doctor please help me .I take pep 96 hours at 30 day after completed pep I take duo test and pcr rna they both are negative. There are 1 spot below my armpit 2 more also same side . Doctor feel on that side lymph node he advise m ultrasound of this side and advice me to check this spot to dermatologist and say if dermatologist say it’s hiv rash then we start hiv treatment . I am not feel any lymph node no fever .only loose weight after pep .he say no test come positive before 3 months.

    Please help me I am in India what can I do can believe on my test or doctor

    • I would trust in your tests, as I’ve told you about 20 times. There is no way to diagnose HIV just by looking at a rash. Your doctor seems more paranoid than you.

  18. sandeep

    Doctor please help me

  19. dr. can I get a hiv by oral sex ?

  20. hi dr . I have make the 4th generation test after 26 days .
    and it was negative , is it like conclusive ??

  21. Dear Dr, I had a possible exposure and was prescribed PEP immediately at the Emergency, here at the USA. My first dose of PEP (Truvada/Isentress) was within 4 hours of the possible exposure. I completed the PEP with tight adherence for 28 days and took an ag/ab test 6 weeks post exposure (i.e. 2 weeks after PEP). The results were negative. My Dr says the results are practically conclusive, but I would need an ag/ab negative confirmation at 3 months. Do you envision the results changing? In other words, do you think the results are good?

    • I believe the results are conclusive. There have been no cases of a negative case 2 weeks post-PEP turning positive later. The 3 month test is still recommended by most institutions but it is largely precautionary.

  22. Hello Doctor, I need your advise. I am a male of 27 and was involved in a protected encounter with a masseuse in a spa on 12th of May. It was protected all the time. But after 2 weeks I had severe sore throat which continued up to 10 days. Since then I am feeling swollen lymph nodes in neck which are hurting a little and are still perpetrated. Also, I have minor rash on my right hand.

    Are these symptoms of Acute HIV Infection or Seroconversion?

    Also, I did 4th Generation HIV Combo Test (HIV1/2 +P24 Antigen) on 18th, 24th, 29th and 44th day after the possible exposure and all came out non-reactive with values 0.04, 0.05, 0.07, 0.09 respectively. As you can see the values are increasing every time. Is this a point of concern? Also kindly help me to decide how conclusive are these results??

    Also one last thing, If I am experiencing the Seroconversion symptoms, shouldn’t I be tested positive??

    Need your advise urgently doctor as I am terrified a lot.

    Thank you.

    • The tests are non-reactive and conclusive. If the symptoms are from seroconversion, the tests would be positive. You do not have to worry.

      • Dear Doctor,

        Thanks for your reply. I really appreciate your efforts to calm me down. But even after your reply I was really worried and went for another HIV Combo Test 75 days Post Possible Exposure. The Results were Non Reactive with 0.07 Value.

        I want to ask whether this test or conclusive? or should I go for another test at 90 days as the guidelines?

        Need your advise.


  23. shobhini

    I am extremely worried 4-5 years ago I had a high risk of vaginal exposure with someone whose HIV status was unknown to me. After 5 years , last month of May, 2017 i decided to take a test in Mumbai, India where I reside. I went to a reputed lab and got myself the latest fourth generation test and also a pcr HIV 1 viral load test. All were negative and pcr viral load test of HIV 1 was undetectable completely. Since then I never indulged in any such activity which could make my window period confusing. The last exposure was 2012 and since then in the year 2017 I tested directly through HIV 4th gen, HIV 1 pcr viral load and western blot for HIV 1 and 2. All came negative but the only thing which I am concerned about is HIV 2. What if I am a negative sero- negative , my antibodies are not coming even after 5 years and the test which I took was of HIV 1 viral load and p24 antigen but not of HIV 2. HIV 2 antibodies I did and it came as negative but what if I have a genetic immunity problem and this is not making my antibodies to appear for HIV 2 as well. I was reassured of my HIV negative status however now I got worried again thinking what if I have HIV 2 and what if my antibodies are not being detected due to some genetic or immunity problem. Is there a possibility doctor? My humble request to you is please read my question and kindly reassure me of my status , can I move on in my life permanently and concentrate on other things such as my career and my family ? Are my tests after 4-5 years of exposure 100% conclusive ? Is there a chance for me to be sero-negative although it is extremely rare of not being able to detect HIV 2 antibodies? I am confident of my HIV 1 negative status but am a bit nervous about HIV 2 status. I don’t feel like taking more tests as I have already given much of my money for different testing s still not able to assure myself of HIV 2. Please please please reply i am begging you.

  24. Alvin Poo

    Dear Doctors,

    I have read about articles claiming that Oraquick has 92% sensitivity, but some sources also said 99%. Why is that so?

    I have also done an Oraquick 3 months after an incident but I gargled with water 15 minutes before. Also, I have done the same Oral swab 6 months later after the incident. Both are negative. Should I move on?

    And is it even a risk, I was afraid that doctors reuse a lancet and have you heard of any transmission cases in the world from this?

    Thank you so much.

    • I suppose it depends on the study. So the sensitivity range may have varied between the different studies. I believe that two tests is more than enough to confirm your negative status. And no, we do not have re-usable lancets nor have there been any case of HIV infection from contaminated lancets.

      • I took a HIV combi PT test more than 40 days post exposure and it came out Negative 0.392COI <1. My risk was from kissing outside her vagina and I gave her a handjob. She also gave me handjob. No Vaginal sex happened. I took another Combi PT test yesterday and doc said the result came out today. So if it comes out NEGATIVE (more than 63 days post exposure), can I really move on with my life or do I need to take a confirmative test at week 12th ? Best regard.

        • The tests are conclusive and do not require further testing. And there is essentially zero risk from your exposure in the first place.

  25. is there any possibility that combo tests are less sensitive to hiv-2 and some subtypes of hiv?

    • No evidence of this being an issue thus far. If you have concerns, please speak to the manufacturers for more details.

  26. hi doctror..i have a question..It seems that test accuracy is almost 99,7%.That means that in 100milion peaople get tested 300thousand will be false negative..can this possible be true?

    • Not necessarily. Most HIV tests will claim extremely high sensitivity, meaning low to nil numbers of false negatives, but may have relatively lower specificity, meaning few cases of false positives. This is why any positive result on a rapid test must be sent for confirmatory testing with Western Blot.

      • yes but this rates are for all who ve done the test and are negative? that means that a lot people have the virus and they don t know it doctor…

  27. Hi doc, I had an exposure 31 days ago with a prostitute when my
    condom had a small hole on the neck of the
    condom…I did the elisa/p24 antigen combo
    test at 24 days and the results were
    negative and the doc told me its conclusive but My throat has been irritating since
    2-3 days after the exposure and its upto a
    whole month now and theres no
    improvement..i’ve had a running nose from the
    28th upto 30th day but its now almost gone. am so
    worried it could be hiv..now that i’m on the
    32nd day, should i be less worried or what hiv
    test do you recommend and at which time so
    that i can be totally sure?


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