Q. Kindly advise whether HIV rapid tests cover O type antigen or not.

Answered by
Dr. Goswami Parth Rajendragiri
and medically reviewed by iCliniq medical review team.
This is a premium question & answer published on Oct 30, 2018

Hello doctor,

I have a doubt regarding the HIV rapid tests. I want to know whether the tests cover the O type and another rare type of antigen or they only cover M type. I underwent a RNA PCR, two Duo combo and two antibody tests after a risky exposure. All were non-reactive. What is haunting me is are the tests missing out any rare type? Do they even check for O type? Secondly, most testing kits as I saw on the net are using gp41and gp120 for the antigen. Is gp41 also common for O type or is it for M type only? How to rule out O type infection? Please help.



Welcome to

I have reviewed your query and here is my advise. As far as HIV infection is concerned, M strain variant of HIV1 is a common type. O subtype is very rare. However, let us move onto your question.

Rapid diagnostic test and CMIA usually detect M strain of HIV effectively. However, depending on manufacture, a final comment can be given. But RT PCR usually detects all strain for HIV. Kindly mention after how much time of exposure you have investigated with RT PCR? I am asking this question to rule out window period for HIV.

Thank you doctor,

I have taken PCR test after 12 days, the fourth generation after 32 days, and card tests at 80 and 108 days. All are negative. How to make sure I rule out the O type of infection also? Should I go for a PCR again? Or can I take this test as conclusive? Are gp41 not present on O type of HIV 1?



Welcome back to

I have reviewed your query and here is my advice for your case. RT PCR usually gives effective result after two to four weeks. So you had tested for it earlier. Moreover, CMIA and fourth generation ELISA also rule out HIV effectively after six weeks. But anyways, after three months of infection usually antibodies are developed in enough concentration and so rapid card test can effectively rule out HIV after three months. Now no need for doing PCR testing. It is used if you want to rule out HIV before six weeks. Now no need for PCR testing.

The different kits use antigens that are prevalent in your area, and no need to focus only on O strain. However, advanced HIV CMIA test claims to detect O strain as well. You can investigate with CMIA test just now (after three months of exposure, repeat testing recommended). If it comes negative, then no need to worry and forget about incidence. Gp41 is present over HIV1 type virus and so can be present over subtype O strain as well. You can revert back with CMIA report once done to guide you further.

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