###Human: Kindly advise whether HIV rapid tests cover O type antigen or not. ###Assistant: Hello.  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.