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DUO tests - what is the truth?

There's quite the confusion on the cyberspace, regarding how conclusive and when a DUO test can be. While places like the UK consider a result after 4 weeks reliable and after 6 weeks a conclusive one, countries like Canada only consider conclusive the 3 month test. Why is there such a big difference? Have there been reports of people testing negative 8 weeks after the last sexual encounter only to test positive after 12 weeks, or is this just a precaution companies take? I'm not posing a personal matter, it's a question regarding the GP. I've seen numerous threads asking this. If I may speak personally, my doctor here in Europe told me that a DUO test can be considered conclusive after 6 weeks.
There's also the p24 antigen question. Can the DUO test detect antigens after 6 weeks, given that the antigens stay in the blood for a short period of time? And when THESE disappear, does this mean that antibodies are created, thus the test can detect those? What I'm asking is if the test is going to detect one of those two for sure.

I would like an answer to all the questions I've posed above and not the usual "All tests are conclusive after 3 months". I'm actually trying to expand knowledge here and maybe have a conversation.

9 Responses
Avatar universal
I can tell you here in the US it takes a lot of time and money for tests to be approved by the FDA, where Europe does not have the strict standards as the US. So while the test has been approved for use in the US it is not concluisve until an antibody test is taken at 3 months.

Antigens peak about about 28 days and after that decline while antibodies start to be produced.
Avatar universal
So it has mainly got to do with resources? Which still is not making sense how there's this huge gap. I mean, it would make more sense if the time difference were to be 1 month.

Regarding the second part of your answer. You're saying that while the antigens start declining antibodies start being produced? Does this mean the test would either detect the one or the other? My concern is about what I read, that the antigens can decline and not be detected, but at the same time the test might not detect the antibodies either, which I personally thought is probably false, since I've been told the DUO test is very reliable and sensitive.
Avatar universal
If say day 35 when the antigens are decreasing I believe it is possible that antibodies will not have a high enough production to be found. Now I could be wrong on this so that is why some places will say 6 weeks because by then the antibody production should be high enough. But like I said until the test manufactures and FDA gave a smaller window period for a conclusive test we will stay with 3 months.

DUO test is a very good test and I defer to Dr's when you are taken a test but advice here will be DUO test at 28 days is a good test or an antibody test at 6-8 weeks are unlikely to change but 3 months is conclusive.
Avatar universal
Thank you for your answer. Tell me something else - is the DUO test considered to be more "reliable" than a standard antibody test? Or is the second part of it inferior when it comes to antibody testing?
Avatar universal
The antibody part is the same as a stand alone antibody test
Avatar universal
So we come to my original question? Does the antigen decline mean an antibody production?
Avatar universal
It does
Avatar universal
Which is why I don't get why the DUO test cannot be considered conclusive after 6 or 8 weeks. I mean, if there's a p24 decline, antibodies start being produced, thus the test would be able to detect those. Doesn't the non-detection mean no infection?
Avatar universal
Again it takes a lot of time and $ for the FDA and approve testing changes. If you have millions to give to a company so they can go to the FDA then feel free to do so.
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