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Inconsistency with window period?

Dear All,

It seems to be generally accepted that 4th generation HIV duo / combo tests shorten the window period for detecting HIV infection post exposure .
Many people now believe the window periods for a conclusive result to be :
- 4TH GEN DUO: 4 weeks (or 6 weeks in some cases), i.e. 28- 42 days. This is backed up many UK private practises and even NHS GUM clinics
-  3RD GEN ANTIBODY: 12 weeks for a 3rd gen antibody test, i.e. 84 days. This window is well established worldwide

However, when researching online, most academic papers state that the development of the p24 antigen only precedes the antibody by 5-10 days.

So if the p24 antigen becomes detectable only 5-10 days prior to the antibody, how can the claim be made that the DUO TEST shortens the window period by 42-56 days (6-8 weeks)? Wouldn't it just shorten the window period by 5-10 days?

2 Responses
Avatar universal
Antigen level peaks at about 28 days then the antibody production starts. So while the sensitive nature of modern testing will find the antibodies quicker the approval has not been made for a standard antibody test to be labeled concluisve sooner.
Avatar universal
BASHH/EAGA statement on HIV window period

November 2014

HIV testing using the latest (fourth generation) tests is recommended in the BHIVA / BASHH / BIS UK guidelines for HIV testing (2008). These assays test for HIV antibodies and p24 antigen simultaneously.  A fourth generation HIV test on a venous blood sample performed in a laboratory will detect the great majority of individuals who have been infected with HIV at 4 weeks after specific exposure.

Patients attending for HIV testing who identify a specific risk occurring less than 4 weeks previously should not be made to wait before HIV testing as doing so may miss an opportunity to diagnose HIV infection (and in particular acute HIV infection during which a person is highly infectious). They should be offered a fourth generation laboratory HIV test and be advised to repeat it when 4 weeks have elapsed from the time of the last exposure.  

A negative result on a fourth generation test performed at 4 weeks post-exposure is highly likely to exclude HIV infection.  A further test at 8 weeks post-exposure need only be considered following an event assessed as carrying a high risk of infection.

Patients at ongoing risk of HIV infection should be advised to retest at regular intervals.

Patients should be advised to have tests for other sexually transmitted infections in line with advice on window periods for those infections (see BASHH guidelines                at: www.bashh.org ).


Dr Keith Radcliffe - Chair, BASHH Clinical Effectiveness Group
Dr Laura Waters - Chair, BASHH HIV Special Interest Group
Prof Brian Gazzard - Chair, Expert Advisory Group on AIDS
Dr Jan Clarke – President, British Association for Sexual Health and HIV
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