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.

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.

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

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  1. Caps
    Caps says:

    Hello , if i got tested with a 4th generation after 3 months of exposure and showed negative that means I don’t have hiv ? Thanks

  2. Lee
    Lee says:

    Hi, i had sex with my life partner on the 18th of may. On 19th may, i had a protected sex with another long term partner(not sex worker). We had protected sex initially but she removed my condom and we briefly had unprotected sex for 10min. On 21th may, i had sex again with my life partner again.
    On 24th may, i experienced unrination pain.(can be due to dirty hands touching my penis while peeing as im a technician, hands always dirty). On 28th may, i experienced sore and slight itch on my testicles n penis head n spotted about 5 bite-like spots on my foreskin(slept naked n may have gotton bites from beddings).
    Im really worried n have not gone for 4th gen test as have not passed 14days.

    • afa_v2
      afa_v2 says:

      Hi Lee, these are not symptoms associated with HIV. It may be other Sexually Transmitted Infections (STIs), especially if you notice any whitish or yellowish discharge from your penis and there’s a burning sensation when urinating. We are not able to diagnose anything simply by discussing it here and would strongly recommend a full STI screening.

      • Lee
        Lee says:

        Hi, i have just done my 4th gen text this morning and it showed negative. Its supposed to be the 14-15th day today. May i know how accurate is this result? I know the most accurate will be on the 90days period but the worry and stress is there.

  3. 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.

  4. 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.

  5. 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.

  6. 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?

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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/

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