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

16 replies
  1. 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?

    Reply
    • afa_v2
      afa_v2 says:

      Hi,

      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.

      Reply
  2. 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?

    Reply
  3. 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

    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.

      Reply
      • 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

        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.

          Reply
  4. 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?

    Reply
    • 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.

      Reply
  5. Senthil
    Senthil says:

    Doing a great job. Thanks in advance.
    After unprotected sex with a Massage girl immediately with in few hours I was put on PEP. After 30days of completing PEP I took HIV DUO TEST (CMIA METHOD) which came back
    non-reactive . Is this test is conclusive.

    Reply

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