« Go Back

4 generation hiv test accuracy and p24 antigen detection abilty


I have some query related to the accuracy and conclusiveness of the 4 generation combo testI am a men of age 26 aroundMy question are1.I had a negligible risk exposure as a sex worker just licked and perform oral sex by taking my penis in her mouth .It was unprotected/without condom and for 2 minutes.So i did 4 generation test ....4 times at different time interval.One at 18.5 day after exposure,,one at 30.5 day after exposure...one at 43.5 day after exposure and one at 53.5 day after exposure!!!!!!!!!! All test were non reactive/negative....So my question is that my test was HIV Combi(combination of hiv p24 antigen and anti hiv antibody 1 and 2) performed on fourth generation eclia cobas 6000 (e601) utilizing electrochemiluminescence immunoassay .Is this Eclia fourth generation test as accurate as EIA fourth generation test or elisa fourth generation test ???And is my fourth generation eclia test as accurate to FDA approved HIV 4 generation test which include Abbott Architect HIV Ag/Ab Combo Assay and Bio-Rad GS HIV Combo Ag/Ab EIA.Are all these 4 generation test have the exact same accuracy,sensitivity and conclusiveness.Are all these fourth generation test i have listed are equally best and sensitive???2. As i have heard that most of the HIV specialist and physicians consider 4 generation test to be conclusive at or after 6 weeks after exposure ,if the patient has no underlying major illness and is not on hiv medication or PEP.IS it true???Please confirmEven HIV specialist say result at 6 week from 4 generation hiv are definitive and doesn't need any further test what ever the risk of exposure is high/low doesn't matter.And hiv specialist further quote 4 generation combo test as conclusive at 6 weeks as antibody alone test conclusive at 3 monthsSo as i did my hiv test after 6 weeks and also after 7 weeks post exposure as mention above by Eclia 4 generation combo test.So are my test considered conclusive by hiv specialist .What i meant to ask that only FDA approved 4 generation test are considered conclusive by hiv specialist at 6 weeks or even my Eclia 4 generation combo test(details listed above of the test) which are i don't think FDA approved are also consider conclusive by most hiv specialist??Question 3As i know you all are highly trained volunteers and doing a great job by educating about hiv and related up to date knowledge.I know you are not doctors but still i want to ask something from you.So that you can explain from what knowledge you haveThe thing is that in a 4 Generation Hiv combination test Like mine was performed by Eclia they test for Hiv 1 and 2 for anti hiv antibody and also for p24 antigen.But what i have came to know that they only look for p24 antigen to Hiv-1. The hiv-2 is not included in the p24 antigen test.Ya the antibody portion looks for both hiv 1 and 2 types .But the p24 antigen only looks for HIV -1 type and not the HIV-2 typeSo this could be then possible that if someone is infected with HIV-2 type for instance.And he took a 4 generation.The test could not detect the antibodies as it had not started being produced yet .And the test could also not detect p24 antigen as the individual is infected with hiv 2 type..So could this be one way getting a false negative result.But i thought this 4 generation test was very reliable and sensitive.Please explainQuestion 4I know i must ask this to hiv specialist but it will be very helpful if you could provide some information.As how the hiv specialist consider the 4 generation test to be conclusive at 6 weeks while 3 generation test,hiv specialist consider conclusive at 3 months..with the matter of fact that if someone have got infected with hiv type 2 .And he does a test at 6 weeks with a 4 generation test.The test is negative and hiv doctor conclude it conclusive!!But what if that person had a delayed response of immune system and at 6 weeks the antibodies have not yet formed(and will form later till 10 weeks for e.g) and the p24 antigen doesn't detect hiv type 2.How does the hiv specialist conclude 4 generation conclusive without not taking this factor.I know hiv type 2 is a not commonly found but we cant exclude the possibilities too.Please explain this scenario tooQuestion 5 lastAs i have read several answers on your website and even other website to this type of question.That with a 4 generation test is this possible that when i did a test,,the antibodies have just not started to formed at detectable levels and at the same time p24 antigen have gone to undetectable levels as some antibodies have bind it with p24 antigen but not detectable yet??In simple words could it be possible that both parts of 4 generation test have come false negative...And your website replies and other website replies are that it is not possible for 4 generation test to show false negative on both parts of the test at the same time!!!!plz confirmAnd if it is true then what if someone is infected with hiv 2 type.And when he did the test the antibody were not formed yet so that part was negative and the p24 antigen does not detect hiv 2 type so that was also negative.So this situation explains that the 4 generation test can give both part of test false negative at same time!!!!I would be glad if you would be able to explain about the fourth generation related queries.I know my risk was negligible but i more interested in knowing about the fourth generation related queries.Thank you.And You are all doing a great job!!


Hello and thank you for using the AIDS Vancouver online helpline as your source for HIV/AIDS related information.
Before answering your questions, I just want to note that as oral sex poses no real risk for the transmission of HIV, I do not generally advise spot testing for HIV after having oral sex (or other no/low risk activities). Rather, I recommend that all sexually active individuals opt for regular STI testing for their safety and the safety of their partners. Every 3-4 months is generally a good interval to use.
1.  All fourth generation HIV tests use similar testing methods, and are extremely sensitive and specific for detecting an infection. These tests must also conform to basic quality control, which ensures that regarless of which brand of test you choose you will receive one that is comparable to the others. As such, they are all similarly accurate (sensitivity and specificity). FDA approval applies in the US only; all countries have their own similar agencies to approve the test used in that country.
2.  This is correct. While HIV testing guidelines recommend testing at 12 weeks, most HIV specialists will consider a negative result on 4th generation testing to be conclusive at or after 6 weeks post-exposure. Again, FDA approval applies in the US only; all countries have their own similar agencies to approve the test used in that country.
3.  HIV-1 is by far the most common strain of HIV outside of Africa. In addition, the antibody portions of the tests are more sensitive than they were in the past, allowing for earlier detection. A negative p24 antigen test alone is not conclusive for no current HIV infection, however when also paired with antibody testing at 6 weeks gives an accurate enough result that if both are negative at 6 weeks, most specialists will consider that negative result to be conclusive.
4.  It is true that in rare cases a diagnosis may be missed, but this is true with any condition. In the case of HIV, however, if our recommendations for regular testing are followed (every 3 months) then the infection will be detected in the next test.
5.  If sufficient antibodies were present and binding to the p24 antigen to make that portion of the test undetectable, then the antibody portion of the test would be positive. There is no stage at which both could come back as a false negative. If the person were infected with HIV-2, then one would rely on the antibody portion of the test. Again, since we recommend testing every 3-4 months if you are sexually active, the next test would be able to detect the infection.
I hope this helped to answer your question, please feel free to write back if you have any further concerns.
All the best,
JonathanAIDS Vancouver Helpline Volunteer
Phone: 604.696.4666 (Mon-Fri 9am-4pm)E-mail: helpline@aidsvancouver.orgWebsite: www.aidsvancouver.org/helpline