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Hello, I request your expertise in clearing a doubt that I have regarding HIV. The antigen is the P24 which is produced in the early stages of infection. This p24 antigen is only produced with HIV1 infection and the antigen for HIV2 infection is different - not p24. Although I Understand that HIV1 infection is causing 95% of the problem in this world. My question is although Group M in HIV1 is most common and tests also check for variants of group O. Group N and P being very rare but just in case someone is infected with Group N or P will those types and subtypes also produce p24. Is p24 produced in all 4 groups of HIV1 namely M,O,N and P including all crf’s. I would be highly grateful if you could explain in detail so that I understand.


You’re correct that HIV-1 represents the significant majority of HIV infections across the world. Group M is the biggest group, followed by O.

The p24 antigen / antibody HIV test (also known as the 4th generation HIV test) detects p24 antigens for HIV-1 (Groups M and O), and antibodies for HIV-2. The p24 test does not reflect Groups N and P as they are very rare and not been found outside of Africa.

If you are testing after a potential exposure that you had in Canada, you can feel confident in the p24 test will reflect any strains you could have been exposed to.

If you are testing after a potential exposure you had in Africa, then you may want to seek additional testing.

Please let us know if you have any other questions.

Health Nurse

This answer was posted on April 26, 2018

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