Avatar universal

Duo/Combi Test Question

Hi All

Could someone explain , what reason would the P24 Antigen would not show up in the test at a test done at 21 days. I am confused alittle as I was understanding that the P24 would be always detectable between 14 and 21 days. Some members on the forum have suggested that for certain reasons it would be delayed, or not show.

I hope someone has some knowledge please
8 Responses
Avatar universal
99.9% at 3 months vs 99.8% at 4 weeks.

P24 is the virus itself. The only reason it would be undetected is a very low viral load, which is highly unlikely at 4 weeks. The Vidas Duo can detect 2 virus per mml of blood or plasma.. whatever.. But consider, thousands upon thousands of virema are produced in early infection. Very unlikely to miss an early infection really. I can't really see how at 21 days p24 wouldn't be detected, but maybe it happens very rarely- you should repeat it anyway at the recommended 28 days + for more certainty.

Ontop of that the average time to convert is 22 days.. So most people have actually made antibodys by this point.. You would very unlucky to not have the p24 picked up really. Try and relax!
1163575 tn?1339478617
p24 antigen does not alwis present...it dissapears after some time..
Avatar universal
thanks, I am aware that the P24 will reduce over time , but my question is what are special reasons, which some members speak about (if any) P24 is delayed or never shows, or does P24 always is produced if infection was introduced.
Avatar universal
Test using an antibody test at 3 months to get you conclusive result.
Avatar universal
I am sorry I seem to have posted instead PM on another thread and duplicated my thread... Sorry
Avatar universal
1364665 tn?1291607092
The combo test, which detects both HIV antibody and p24 antigen, is considered virtually 100% reliable at 4 weeks.But still 3 months until completely reliable testing is standard advice. In this advance modern technology, a test of ( both HIV antibody and P24 antigen ) at 2 weeks is assuring ( c0nsidering that you're living in the one of the most advance country ). But still 3 months test is the conclusive.

Avatar universal

Page 27
Current methods for the detection of HIV may not detect all infected individuals. An ARCHITECT HIV Ag/Ab Combo test result that is nonreactive does not exclude the possibility of exposure to or infection with HIV-1 and/or HIV-2. Nonreactive results in this assay for individuals with prior exposure to HIV-1 and/or HIV-2 may be due to antigen and antibody levels below the limit of detection of this assay.

UK testing guidelines.
Post-test discussion

The need for a repeat HIV test if still within the window period after a specific exposure should be discussed. Although fourth generation tests shorten the time from exposure to seroconversion a repeat test at three months is still recommended to definitively exclude HIV infection.

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