Antigen sensitivity and window

Dear all,

The expert doctors at medhelp always say that a combitest antigen / antibody is about 99% secure at 28 days (4 weeks). I am confused since it seems the antigen part of the test has to be taken at 28 days and not beyond?
The antigen is said to decline rapidly after its peak at 4 weeks, but how long would it still be detectable after that, only days or still some weeks?

Yesterday I found out that I had only an antibody test at 28 days, and not a combitest.
I did have a combitest at 6.5 weeks. Would that have been too late to pick up the antigen, making my combitest results meaningless (antigen gone already but too soon for antibody testing).

I have also read that the antigen test would not be reliable for people who are asymptomatic seroconvertors. It would not be present in those cases. Only if one is ill at seroconversion, it would present itself.

Please advice

[NickOne7]

Test using an antibody test at 3 months to get you conclusive result.

[Teak]

http://www.fda.gov/downloads/BiologicsBloodVaccines/BloodBloodProducts/ApprovedProducts/LicensedProductsBLAs/BloodDonorScreening/InfectiousDisease/UCM216314.pdf

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.

http://www.bhiva.org/documents/Guidelines/Testing/GlinesHIVTest08.pdf