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Hi, I have a question about the HIV tests done in BC. My understanding is that the 4th gen duo tests look for the p24 antigen and test for HIV-1 + HIV-2 antibodies. What about different subtypes/groups of HIV? Are all the different subtypes/groups also tested for by the 4th gen duo tests? Additionally, what about the pooled RNA NAAT (i.e. like the one offered at the HiM on Davie), does that look for the RNA from HIV-1 & HIV-2 plus different subtypes/groups? The internet is a scary place and there are reports (in scientific journals, not message boards) about seronegative HIV infections (i.e. a person infected with HIV, but routinely testing negative even past the window period - as far as five months out after last exposure). I was just curious if it is possible to be seronegative and infected by HIV, and be missed by the current routine testing. Thanks for your help!

Sorry about the delay in posting a reply to your question. Due to the technical nature of the question we thought it best to send to one of our doctors with expertise in this area. Here is their reply.

I have a question about the HIV tests done in BC. My understanding is that the 4th gen duo tests look for the p24 antigen and test for HIV-1 + HIV-2 antibodies. What about different subtypes/groups of HIV? Are all the different subtypes/groups also tested for by the 4th gen duo tests?
The serological test is designed to detect all known circulating HIV subtypes. There might be a slightly different sensitivity of detection for some of the rare subtypes which might delay detection of a rare subtype by a few days but the rare subtypes will still be detected. Also, the P24 antigen is expressed by all the known subtypes.


Additionally, what about the pooled RNA NAAT (i.e. like the one offered at the HiM on Davie), does that look for the RNA from HIV-1 & HIV-2 plus different subtypes/groups? The internet is a scary place and there are reports (in scientific journals, not message boards) about seronegative HIV infections (i.e. a person infected with HIV, but routinely testing negative even past the window period - as far as five months out after last exposure). I was just curious if it is possible to be seronegative and infected by HIV, and be missed by the current routine testing. Thanks for your help!
The current pooled and individual NAAT only detects HIV-1 and it will not detect HIV-2 which is very rare in North America and indeed globally. The way we would detect an HIV-2 infection is that the HIV Antigen/Antibody test is able to detect HIV-2 and we use an immunoblot test called the Geenius that is able to detect and differentiate HIV-1 from HIV-2 infections. This is done automatically by the laboratory when such testing is appropriate. HIV-2 NAAT is also available by reference laboratories.
With modern tests and the testing algorithms we use it is very hard to miss an HIV infection.

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Health Nurse

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This answer was posted on February 21, 2017

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