HIV Combo test has screening and confirmatory diagnostic value and the test returns results are available after 4-5 hours (if result is negative). If result is positive the sample needs to be referred to an approved laboratory for further confirmation as per rules of regulatory authorities. 

The HIV RNA is a quantitative assay testing done by PCR technique that helps to confirm and quantify the HIV infection and know the viral load of the positive patient. It can be used as an initial test before starting the treatment and a follow up test to monitor the effectivity of the treatment over certain time intervals.