Anonymous
46 days after the risk I did a test that said the following:
Anti hiv 1 + 2 and negative p24 antigen
Method: Electro-chemiluminescence
This test is based on the simultaneous determination of IgG anti-HIV1 and anti-HIV2 and antigenaemia p24, which allows to reduce the delay between contamination and virus detection.
According to what you have mentioned before, the test that combines the search for antibodies and antigens at the same time is of 4 generation and the window period is 6 weeks in 99% according to many experts. The question I have is that in my test it says: Anti HIV 1 + 2 AND ANTIGEN P24 NEGATIVE
Method: Electro-Chemiluminescence and after says: This test is based on the simultaneous determination of IgG anti-HIV1 and anti-HIV2 and antigenaemia p24, which allows to reduce the delay between contamination and virus detection. I have read that those of 4 generation usually look for igG and igM and p24 antigen. Could it be that my test only looks for IgG and p24 antigen or have IgM ignored or is it normal? Is it still 4 generation to look for antibodies and antigens? Can I stay calm for being 4? Thank you very much for your help andgreetings from barcelona, you do a magnificent job
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Anonymous
Hello,

Thank you for your inquiry. From what we gather from the question, you were asking about specific details on the HIV 4th Generation Test and what is detected by the test.

The reading that you have conducted seems to be accurate, as most 4th Generation Tests are said to test for both IgG and IgM antibodies to HIV-1/2 as well as the p24 antigen present on the HIV virus. The inclusion of the IgM antibody detection in some HIV tests is used as a method of identifying earlier infection compared to IgG antibodies. The detection of IgM has a similar window period to the detection of the p24 antigen, but the detection of the p24 antigen is much more reliable as some people do not have an initial IgM antibody response to HIV (1). Many 4th Generation Tests do not describe the specific type of antibody tested, but they all test for HIV antibodies as well as the presence of HIV antigens (p24 or NAAT) (2). In the test you received, they either did not test for the IgM or they did not specify that the presence of the IgM antibody was tested.

As shown by the graph included in this post, the initial high point of the antibody line shows the rapid production of IgM antibodies after HIV infection. The line then decreases, but quickly goes back up as the production of IgG antibodies ramps up. If you notice, the initial high point of the antibody line is quite similar to the p24 antigen line. If the test you received only detected the IgG antibody to HIV-1/2 in addition to the p24 antigen, there is still sufficient accuracy of the test within the provided 4th Generation window period.

Regards,

AIDS Vancouver Helpline/Online, Marie



[Patel P *et al.* (2012) *J Clin Virol*](https://www.ncbi.nlm.nih.gov/pubmed/22381919)
![HIV Window Period][HIV Window Period]
[HIV Window Period]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6195213/bin/nihms867488f1.jpg

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