An antibody test at 3 months post exposure is the only approved HIV test. PCR-RNA and P24 tests are supplemental tests used in conjunction with an Antibody tests. That can be a standard ELISA or a Rapid HIV test which is also an ELISA test.
Under what circumstances is a PCR-RNA and P24 test used and does that give you a more conclusive result?
Both tests are to help with early detection, they don't give you a conclusive result at all.
Yes the antibody does without the added expense of any supplemental tests.