What is a 4th gen HIV test?

The AFA Anonymous Testing Services have been providing simple, quick and affordable HIV testing utilising 3rd generation test kits for both blood and oral fluids. In an effort to improve our services, the AFA anonymous testing clinic and mobile testing services will be introducing the 4th generation test kits.

What’s the difference between 4th and 3rd gen test kits?

Fourth-generation tests kits look for both antibodies AND antigens.

  • P24 Antigens are proteins on the surface of the HIV particle.
  • Antibodies are produced by the immune system in response to the HIV antigens. They fit together like a lock and key.


Immune response of HIV infection

3rd generation tests take 6-8 weeks and only tests for antibodies.

4th generation tests are accurate 14 days after exposure, because this is when the p24 antigen becomes high enough to measure; effectively reducing the window period by average of 14 days.

A negative result at 28 days is good news but it is not conclusive. UK guidelines (BASHH) say that an early negative result at 28 days (1 month) needs to be confirmed with a second test 90 days (3 months) after the exposure.

Ask for the 4th Generation Test at one of the following services provided by AFA at $40 per test.

Click to learn more about each service.

More about p24 antigen

One distinctive HIV antigen is a viral protein called p24, a structural protein that makes up most of the HIV viral core, or ‘capsid’. High levels of p24 are present in the blood serum of newly infected individuals during the short period between infection and seroconversion, making p24 antigen assays useful in diagnosing primary HIV infection.

Antibodies to p24 are produced during seroconversion, rendering p24 antigen undetectable after seroconversion in most cases. Therefore, p24 antigen assays are not reliable for diagnosing HIV infection after its very earliest stages. However, HIV infection can be reliably diagnosed earlier with combined antibody/antigen tests than with purely antibody-detecting tests, and fourth-generation antibody/antigen tests are now the standard screening assay in the UK and some other countries.

More about HIV antibodies

Antibodies are protein molecules produced by the immune system in response to allergens, infectious organisms (including viruses, bacteria, fungi and parasites), and sometimes (in autoimmune disorders) the body’s own components.

Infectious organisms and allergens display characteristic proteins called antigens. The immune system recognises and responds to antigens by generating corresponding antibodies. An antibody is designed to ‘fit’ only one particular antigen, rather like a key in a lock. (The word ‘antigen’ in fact derives fromantibody generation.) By locking on to the antigen-bearing intruders, antibodies aim to render them harmless, to kill them outright, or to ‘tag’ them for destruction by other components of the immune system.

One or two weeks after initial exposure to HIV, antibodies to HIV antigens begin to appear in the blood, at concentrations which continue to increase for several more months. These antibodies persist for life, providing distinctive markers which can be identified by HIV screening tests

66 replies
  1. Sati
    Sati says:

    Hai sir,,,, last month I go to body massage spa,, ending time that girl do unprotected oral sex,, in 4to 5 seconds only,, suddenly I stopped her,,, then I go to shower quickly,, so I many worried,, sir,,, 10 days after one time check in blood 4th generation testing,,, results is normal,, again I tested in 18 days it also normal,,, at your afa clinic,,, so I one more time I need checking ?? Please sir

    • afa_v2
      afa_v2 says:

      There is little risk to the activity, but like many here, if you have not done a full STI screening, we will strongly recommend you too. It is normal for many to experience some levels of fear after visiting massage parlours or a venue where indirect sex workers are at. Many people visit these places, and there is no shame in it, it’s a normal human need.

  2. Tag
    Tag says:

    I have a protected sex but not totally erected last march 6 2018 with a pay for sex lady. I tested non reactive at my 4 days after exposure and last april 1 i tested non reactive for both 4th gend and 3rd gen sd bioline hiv 1/2. At 25days post exposure non reactive result for 4th generation is it conclusive?

    • afa_v2
      afa_v2 says:

      Hi Tag, this is not conclusive, i’m surprised that your counselor failed to notify you that, basically, testing at 4 days is not accurate at all. That test only cleared you for any potential exposures that took place 6 weeks ago. Not the immediate one on Mar 6. You should test 42 days after your exposure with a 4th gen test, or 3 months after the exposure if you are using the 3rd gen test.

  3. Justin
    Justin says:

    I had exposure on jan 04 i had sex with csw suddenly condom was broken but i didnot ejaute inside her later i clean the penis with towel and i stop sex and after 1 week i had sevier stomach pain beacuse that is my first sex exposure later i decided to take hiv test at 7 days it came back negative hiv1&2 4th generation .at 26 days i take another test of Hiv1&2 hbsag HCV it all came back negative and i decided to take another test at 8 week of tridot test it also came back negative and i finally decided to take 12 week (86days) tridot test it also came back negative now i m having right jaw pain and high fever and head ache it due to HIV please tell me doctors i really.confusing

    • afa_v2
      afa_v2 says:

      While it is considered a low risk activity, we will recommend you to test if you have been sexually active and have not tested in the last 6 months.

  4. Hasu
    Hasu says:

    Hello, i had risky exposure with a guy on 3rd feb 2018 nd after that i have been testing regularly at feb 13, march 5th and march 25th all being 4th gen combos, and all were simply non reactive, when should i get another test done?

  5. Sofyan
    Sofyan says:

    Hi, I am from Indonesian.
    On December 28, 2017 I action at risk of HIV-infected, on March 21 2018 (12 weeks/84 days) I test method 1 CMIA with the results of Non-Reactive.
    my question :
    1. Is such tests are the final result ?
    2. Do I have to do retest?
    3. whether the CMIA method is 4th generation ?

    • afa_v2
      afa_v2 says:

      Chemiluminescent microparticle immunoassay (CMIA) test is a reliable, accurate and standard method. It tests for P24 antigen as well as antibodies to HIV1 and 2. The accuracy of this test is 99.9% after three months post exposure. This is similar to 4th Gen test kits, and since you’ve tested 3 months after your exposure, and if you have no other unprotected exposures between those dates, there is no need to retest.

  6. Shouldnt have done it
    Shouldnt have done it says:

    Hello. I just had an encounter today and am already starting to feel uneasy. Potential exposure goes like this:
    1) unprotected oral sex for about a minute
    2) protected sexual intercourse
    However, after ejaculating in her with the condom on, i did not pull out immediately and stayed in her for another minute.
    Based on the above, can you pls let me know if its a high risk exposure? Meantime, im gonna abstain from sex till im 100% cleared from this. Will a 4th gen test on 28th day after exposure a conclusive one?
    Thank you.

    • afa_v2
      afa_v2 says:

      Hi, it isn’t a high risk exposure as long as you’ve used the condom correctly. Not withdrawing immediately carries little risk as long as you’re not exposed to any body fluids. She, however, is at a higher risk than you are.

  7. Dmitriy
    Dmitriy says:

    Hello. I had oral contact with a woman (cunnilingus) on January 27, 2018. 10.02 after 2 weeks passed PCR RNA method, negative. Then 24.02 passed the ab / ag combo, also negative. March 10, I again gave PCR RNA and ELISA ab / ag, this is 6 weeks already – negative. Tell me, is it worth testing for 12 weeks?
    At me it is simple with 10 days a throat red, vision has fallen for these 1.5 months, muscles hurt, diarrhea time through time goes.
    I’m afraid this is already an acute HIV went, just tests did not see it.
    I’m just really afraid that I will have a positive result in 12 weeks.

  8. Ceti
    Ceti says:

    Hi there, I took a 4th gen test at 10 weeks after posible exposure and it came negative,how accurate is it?Because i didin’t test at 4 weeks and i read that the antigen might drop to undetectable levels after the acute stage.So now I’m wondering if the test didn’t pick up the antibodys yet.

    • afa_v2
      afa_v2 says:

      Fourth-generation HIV tests can detect HIV infection in 50% of people by 18 days after infection; 95% of people by 34 days after infection; and 99% of people by one and a half months after infection.

  9. camellia
    camellia says:

    Hi. I had a HIV test done recently using ECLIA method and the results came out as “not detected”. The problem is I only found out that the guy I dated 7 years ago had multiple partners. My question is:
    1) is the results reliable after 7 years post exposure
    2) do I need to take another test

    • afa_v2
      afa_v2 says:

      Hi the result is reliable, the window period of your test is 3 months. As long as the exposure is more than 3 months ago, the results are reliable.

  10. babu
    babu says:

    Hi, I recently had a quick encounter with an escort at a party. She gave me oral sex and then in-service vaginal sex. I wore the condom throughout and there were no signs that it broke or tore during the process. This is the only time I have had sex outside of my relationship. Please let me know when is the earliest I can test and what are the timings of your clinic – also if I need to take prior appointment.

    • afa_v2
      afa_v2 says:

      Hi there is no need for any appointment, our clinic operates on a first come first served basis. Please wait for at least 14 days after your exposure before requesting for a test using a 4th generation test kit.

  11. Marko
    Marko says:

    I have been tested after 45 days from exposure using 4,th gen test. Anf its not reactive. I got .10 out of 1.0 cut off value.
    Dont know what it means.

    Should i have to be worried because i undergo testing 45, days after and not within 28 days.. ?

    Should it has to be within 28 days? Doing test after 28* days is not as accurate as within 28 days..

    Pls respond. Many thanks

    • afa_v2
      afa_v2 says:

      Hi Marko, while we don’t know how to interpret the ‘.10 out of 1.0 cut off value’, but essentially, the more days between your exposure and the test, the more accurate your result will be. So 45 days is better than 28 days. If you tested at any of the 10 anonymous clinics, your test would have been administered using a rapid test kit. These test kits cannot detect the presence of the virus itself, but the antigen, which is a core protein of the virus and the antibodies that your body produces if HIV is present in you. Therefore, there are window periods associated with these sort of test.

      The window period for a 3rd gen test is 28 days and 14 days for the 4th gen test.
      Testing WITHIN the window period means your test will not be accurate.
      For more information please visit :http://afa.org.sg/whatwedo/support/ats/moreinfo-ats/

  12. Joni22
    Joni22 says:

    Hello dear please help me .i have handjob with hiv positive person person without condom.i have done hiv combo test after 19 day 32 day 53 day 82 day and 130 day all came back negative .please tell me i nead more test .i have white tounge and bad taste my mouth please help me.

    • afa_v2
      afa_v2 says:

      Hi Joni,

      Persons living with HIV, who are successfully on treatment, are not walking dirty, bio weapons. Please do not fear us like we will melt you from within. Once a person is successfully on treatment, and has a undetectable viral load, the risk of transmitting HIV is negligible.

      Back to your question. If you have abstained from all forms of sexual behaviours since then, and have tested, your results will be conclusive, and you need not worry that you have contracted HIV. If you however, remain paranoid about this incident, you may want to make an appointment with our counsellors who will be happy to talk to you about the underlying reasons that may be causing you the anxiety.

      Please drop us an e-mail at info@afa.org.sg or call our hotline at 62540212 if you need to speak to someone.

  13. Stan
    Stan says:

    Hi doctor,
    1)I recently fingered a girl. In the midst of fingering, my hand scrapped against the seat surface which caused it to have fresh cuts, which came into contact with the vagina and vagina fluids and my fingers with the vaginal fluids accidentally came into contact with my lips. Am I at any risk of hiv?

    2) Frenched kisses with ulcers in my mouth and tasted blood

    3) fingered a girl and I touched my penis straight after

    please evaluate the risks of my activities!

    I have been having Blur vision, weakness, feeling cold easily, a little dizzy at times, pain near the hips after urination at times, occasional groin discomfort, stomach discomfort, small black dots on my penis

    Not sure if it is anxiety and guilt or am I really at risk??

    And also,
    4) how accurate are the tests for hiv?

    • afa_v2
      afa_v2 says:

      Hi Stan, we’re not doctors, and will recommend that you visit our van or clinic to speak to a take a test 14 days after your exposure. The risk isn’t very high, but with all sexual acts, there is a certain amount of risk involved.

      The symptoms you’ve described are not generally linked with that of an HIV infection, however, if you’ve not had a FULL STI check up in the last 12 months, we will strongly recommend you to do so. You may visit any of your doctors, polyclinic or the DSC clinic which is one of the cheapest option.

  14. Jorge
    Jorge says:

    I had protected sex with a sexworker but when I removed the condom I touch it with a very small injury that I made w hours before when I removed a small piece of hard skin is that a risk? I had a 4th generation test 28 days after and is no reactive but I had some symptoms.
    Please I will wait your answer.

    • afa_v2
      afa_v2 says:

      Hi Jorge,
      The skin forms a protective layer over small superficial cuts very quickly, and unless it’s a big, fresh, open wound that happened immediately before you removed the condom, there is relatively very low risk based on what you’ve described. Symptoms associated to HIV can be tricky, as they are very common symptoms associated with other viral infection. The best way to know, is through taking a test, and your result is negative.

    WORRIED MAN says:

    Hi Sir,
    I had protected oral sex with sex worker 15minutes and protected Vaginal sex 1minutes and also i touch her vagina with my hands.
    This kind of activities what is the HIV risk?. I want to do Hiv Test Hiv P24 antigen test. What is the best time to do.please advise.

    • afa_v2
      afa_v2 says:

      Hi Worried man,

      what do you think the risk level is? There are many ways you cannot contract HIV, that includes practicing safer sex, which you have done so in this incident. You will have to clear the 14 day window period before you can take a P24 antigen test.

  16. James
    James says:

    Hello my last recent partner was over 4 years ago I had a IV gen test with blood over a year and a couple of months since that partner tested negative for all sti. Am I good?

    • afa_v2
      afa_v2 says:

      If you tested at our either our clinic or the Van, our counsellors would have been in a better position to give you this answer.

  17. sunil
    sunil says:

    I had a protected vaginal sex with a casual sex worker on 24 December and after the ordeal I noticed that her menses was just starting plus the fact that I had an irritated follicle on my scrotum just the size of a pimple. I have done rapid hiv test(determine, unigold) on the 6th, 7th and 8th week and they are all negative. My question

    1. What is my expose risk if the blood came in contact with the follicle?
    2. How accurate are the rapid test i took?

    • afa_v2
      afa_v2 says:

      Hi Sunil,

      1. There is very minimal risk in the sexual activity that you have engaged in.
      2. we can’t comment on unregistered rapid test that are not conducted at our clinic or service. If you come to AFA for rapid test, negative by 6 weeks will be very reassuring, but we would suggest another one at 3 months.
    • afa_v2
      afa_v2 says:

      Protected sex generally carries very low risk, if the condoms are correctly worn and removed. If you have not taken a test recently, we will always recommend a test.

  18. Debanshu
    Debanshu says:

    Hi .. I did 4th generation test after 4 weeks and it came negative .. when is the right time to test again … Is it 6th week from intercourses or 6week from the last test .. pls let me know ..

      • Debanshu
        Debanshu says:

        Thanx a lot for your valuable answer doctor .. did test on 9th November and then 22nd November … So next test will do either on 5th Jan which is 90 days from exposure ( sex date ) or January 22nd which is 60 days from my last test ..

        I have one more question .. pls clear it .. on first test after 4weeks index value was 11 and after 6th week test it came 13 .. is it normal or have any worry in that pls pls let me know

  19. Hayden
    Hayden says:

    Hi, I have tested negative for a period of 10 months with no new risks during this time period. Last risky situation was December 2016. Sex with a sex worker using a condom. However I keep experiencing symptoms which I align to acute infection.Tests included Rapid tests (Alere Determine,Unigold and SD Bioline 1&2 3.0) and 4th generation tests. Last test was October 7th. 2017.
    Do you think I need to continue testing for this encounter?

    • afa_v2
      afa_v2 says:

      Symptoms associated with HIV are very common symptoms associated with a viral infection. If you have taken a test recently, we can safely rule out HIV as a cause. We’ll always recommend anyone who is sexually active to test regularly. How regularly depends on how sexually active you are.

  20. tim
    tim says:

    i had unprotected oral sex from a man. he was doing it for me. i didnt do it for him. we also made out. is there any chance i could have gotten HIV? i do not know if he is clean or not.

    • afa_v2
      afa_v2 says:

      If he showered before you had oral sex, I suppose he will be clean. Most of my friends living with HIV/AIDS, including myself, are very clean people, they shower, and take personal grooming as seriously as you and I.

      The correct term to use, is simply, “if he has HIV, or an STI”. If you are receiving oral sex, your risk is generally low. He is at a much higher risk of contracting HIV. That being said, there are still risk associated to other STIs. If you haven’t had a screening for other STIs, we will strongly recommend that you consider one.

  21. Clause
    Clause says:


    Good morning! I had one high risk exposure on 5th Sept, I have done a few tests on:
    1) 7th Days post exposure – 4th Gen Ag/Ab – Non-Reactive
    2) 10th Days post exposure – 4th Gen HIV 1&2 Ag/Ab (ECLIA) – Not Detected
    3) 41th Days post exposure – 4th Gen HIV 1&2 Ag/Ab (ELISA) – Non-Reactive

    Is my result conclusive? Do you recommend 3-month mark re-test?

    Thank you for your time.

  22. Sarra
    Sarra says:

    I don’t have any sexual relationship I went to the medical care to have HIV test and it was negative but after that I was worried what if the Lancet was by a + hiv and it reused on me .I retest again (the rapid test )after a month and it was negative .does it enough or should I take another one.

    • afa_v2
      afa_v2 says:

      Hi Sarra, most lancets are designed for single use only, and there are strict protocols put in place to ensure that contamination is minimized. If you do not have any sexual relationship, then there is no risk of contracting HIV, unless you’ve been exposed to other body fluids, through perhaps, tattoo, receiving tainted blood or organs transplant. Otherwise, day to day casual contact carries no risk at all.

  23. Trina
    Trina says:

    Celibate for 3 years but have had unprotected sex with 3 partners on separate occasions prior to the 3 years. Would like to take a test, is this possible with AFA?

    • afa_v2
      afa_v2 says:

      Hi Trina, yes this is possible. Do note that our clinic will be closed on the 28th. If you have not been exposed to any body fluids that may transmit HIV, then there is no risk at all.

  24. John
    John says:

    Hi. I got tested at the doctor’s office with a rapid test and it came back positive. I went to another clinic and got tested again with another rapid test and it came back negative. Both required blood samples. Could the first one be a false positive? Or what’s going on?

    • afa_v2
      afa_v2 says:

      It could very well be a false positive, however that rarely happens. We would recommend that you consider either taking another test of a different brand, and possibly following up with a western blot test if necessary.

  25. Sandy
    Sandy says:

    Hi I had 4 th gen test at ur clinic i took test after 14 days and it turns to be negative how much percentage it is conclusive plz reply

    • afa_v2
      afa_v2 says:

      Hi, how conclusive the test is depends on your risk of exposure, however, we generally recommend that you test again 4 weeks after your exposure.

      • Sandy
        Sandy says:

        I had unprotected oral sex and protected anal sex I have done 4gen test after 29 days it was negative how reliable is this plz reply

        • afa_v2
          afa_v2 says:

          A negative result from a 4th Gen test at 4 weeks post exposure is very reassuring/highly likely to exclude HIV infection. An additional HIV test should be offered to all persons at 3 months (12 weeks) to definitively exclude HIV infection. Patients at lower risk may opt to wait until 3 months to avoid the need for HIV testing twice.

  26. Fred
    Fred says:

    I haver been tested with 17 days after the exposure. The test was Elisa 4th generation Ab/Ag. The result was negative, is it conclusive?

  27. Mateo
    Mateo says:

    I might have exposed to the virus on the 5th of August. May I know when would be a good time to have the 4th generation test? Would 14 days be long enough to yield an accurate result?

    • afa_v2
      afa_v2 says:


      we would recommend to wait at least 15 days before taking a test. Please refer to our simple guide found here to help you make a decision.