Thanks for the great work you do in answering the questions on the forum.
I have a question regarding the Duo test. I had a fairly low risk encounter 7 weeks ago and had an INSTi at 30 days (negative), another INSTI at 40 days (negative) and blood taken for a combined p24 Ab test on the same day day 40 which was also negative - (I couldn't wait 24 hours without having an idea hence the two tests on the same day). Reading comments on other sites including the USA part of Medhelp has now left me in some confusion.
1. The p24 / Ab test I assume was a Duo? It was done through a private doctor in Birmingham and sent to a Birmingham lab. Would all the labs be using the latest Duo or are there many using older versions? I appreciate you cannot give a definitive answer.
2. I was given the same advice as you quote regarding the accuracy, however, reading on the Medhelp site there are many posters saying that Duo is not conclusive and only an antibody at 3 months is. This seems to be the widely held belief in the US and the NHS and even the BHIV who say that for definitive results 3 months is conclusive.
3. The information in the public domain seems to concur with the 99.89% accuracy in known HIV samples, however, no mention is made of the 28 days in any research paper I can find. It seems that the research has been on known samples but NOT necessarily at 28 days?
4. Is the p24 antigen produced from about day 10 in all cases or is it only produced when seroconverting, i.e. if someone converted after 6 weeks they would not have any p24 at 28 days an hence would be negative at that stage?
5. Are my tests as conclusive as 99.89% at 40 days wrt the above? Would I have had p24 detectable if I hadn't seroconverted yet?
6. In your experience has a negative combo test at 28 days ever turned positive later?
I've copied and pasted your question beneath to make it easier to respond individually:-
I have a question regarding the Duo test. I had a fairly low risk encounter 7 weeks ago and had an INSTi at 30 days (negative), another INSTI at 40 days (negative) and blood taken for a combined p24 Ab test on the same day day 40 which was also negative - (I couldn't wait 24 hours without having an idea hence the two tests on the same day). Reading comments on other sites including the USA part of Medhelp has now left me in some confusion.
1. The p24 / Ab test I assume was a Duo? Yes it would beIt was done through a private doctor in Birmingham and sent to a Birmingham lab. Would all the labs be using the latest Duo or are there many using older versions? Hmmm - I doubt taht all the labs would be using the same but the DUO itself is a 4th generation test which by definition is newer so I would be happy to rely on itI appreciate you cannot give a definitive answer.
2. I was given the same advice as you quote regarding the accuracy, however, reading on the Medhelp site there are many posters saying that Duo is not conclusive and only an antibody at 3 months is.Well, both sides are correct! An HIV DUO test has an accuracy of 99.89% at 28 days or more. If the person has a high risk exposure - penetrative sex with someone known to be HIV positive - and then has a negative DUO but at the time of the DUO develops symptoms convincing of a real possibility of a seroconversion illness = simultaneous whole body rash/sore throat and high fever then we would err on the side of extreme caution and repeat after 7 to 10 days. The result at that point would be conclusive. The three month mark is conservative and out of date - but more importantly it refers to the third generation tests - not the DUO This seems to be the widely held belief in the US and the NHS and even the BHIV who say that for definitive results 3 months is conclusive yep - but for the 3rd generation antibody only tests.
3. The information in the public domain seems to concur with the 99.89% accuracy in known HIV samples, however, no mention is made of the 28 days in any research paper I can find. It seems that the research has been on known samples but NOT necessarily at 28 days? The research is done as you say on samples known to be HIV positive with clear start dates for the exposure giving an accurate time sequence for the testing
4. Is the p24 antigen produced from about day 10 in all cases yes - it is distinct from seroconversionor is it only produced when seroconverting, i.e. if someone converted after 6 weeks they would not have any p24 at 28 days an hence would be negative at that stage? p24 is a viral protein - after HIV enters the target cells it produces large amounts of p24 - p24 is not related to production of antibodies
5. Are my tests as conclusive as 99.89% at 40 days wrt the above? you are a certain HIV negativeWould I have had p24 detectable if I hadn't seroconverted yet?absolutely - as above - but also well over 99% of people will form antibodies by end of week 6 - and you had an INSTI at that point which in our experience is a very sensitive 3rd generation test
6. In your experience has a negative combo test at 28 days ever turned positive later? extremely rarely and in the very few cases there has been confusion regarding the date and extent of exposure
Thank you for your clarification but I am sure you are aware of all the differing advice and guidelines out there on the internet. The web is a useful resource but you don't know what facts to trust, for instance I came across a site that was suggesting a 53% error rate in some third generation tests!
Can I just check I understand you correctly, the p24 is produced no matter whether you have sero converted or not and would theoretically be detectable from about 10 days but the 28 days is to allow for sufficient quantity to be present to show in the tests, therefore the test is just (or near enough) as accurate as a traditional antibody test at three months (or 6 weeks)?
There would be therefore be no chance of a healthy individual with normal immune system not producing p24 in detectable quantities by 28 days or in my case 40?
The only reason I ask is my private GP (who is a fan of your site and says he gets a lot of information from it!) said he was under the impression that the p24 was only produced during the sero conversion stage.
Can I just check I understand you correctly, the p24 is produced no matter whether you have sero converted or not and would theoretically be detectable from about 10 days but the 28 days is to allow for sufficient quantity to be present to show in the tests, therefore the test is just (or near enough) as accurate as a traditional antibody test at three months (or 6 weeks)?correct
There would be therefore be no chance of a healthy individual with normal immune system not producing p24 in detectable quantities by 28 days or in my case 40?Chance is random. A woman in the Lake District bought a box of eggs from her local supermarket and when she cracked each of the six eggs open she found all 6 had double yolks. The chances of this happening is 1 in 1 trillion. So therefore there is a chance of most things happeneing - its just that in reality they are extremely unlikely
The only reason I ask is my private GP (who is a fan of your site and says he gets a lot of information from it!) said he was under the impression that the p24 was only produced during the sero conversion stage. No, you're confusing two different things. The p24 is a byproduct of HIV replication - and indicates viral replication only. Seroconversion is the formation of antibodies - recognition by your body that HIV is present and its response to rty to eradicate it. As the initial phase of replication is immense, huge quantities of p24 are produce. Your immune system will then begin to attempt to get a grip. Over the next few months the viral load - the amount of free virus in your blood - will fall. As it falls so does the amount of p24. Antibodies however will remain. In HIV positive patients who are completely suppressed using antiretroviral medications p24 is harder to find but antibodies are present.
Hi
I have recently read that a problem with the DUO tests is that there may be a second window period due to the disappearance of p24 and non emergence yet of antibodies. Could this apply in this case, a test at 40days, 2 days short of 6 weeks? Would p24 have fallen by this time to an undetectable level and therefore the test being no more accurate than a 3rd gen test?
Many thanks, sorry for the extra question, just trying to put my mind at rest, I know in my heart that repeated testing is not the answer and am just trying to put it behind me by having the best understanding I can.
No, you're confusing two different things. The p24 is a byproduct of HIV replication - and indicates viral replication only. Seroconversion is the formation of antibodies - recognition by your body that HIV is present and its response to rty to eradicate it. As the initial phase of replication is immense, huge quantities of p24 are produce. Your immune system will then begin to attempt to get a grip. Over the next few months the viral load - the amount of free virus in your blood - will fall. As it falls so does the amount of p24. Antibodies however will remain. In HIV positive patients who are completely suppressed using antiretroviral medications p24 is harder to find but antibodies are present.
p24 query
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