http://www.metrokc.gov/health/APU/rna-testing/
RNA testing is not a substitute for antibody testing. It’s a good additional test for those who may have had a recent risk (within the past 1 - 4 weeks) for HIV.
http://www.medhelp.org/posts/show/580324
PCR or RNA tests. Polymerase chain reaction (PCR) tests involve evaluating a blood sample for genetic material — RNA or DNA — produced by the HIV virus infection. These tests measure the amount of virus present in your blood (viral load) and are most useful for monitoring your condition after you've already been diagnosed with HIV. The tests may return a false-negative result if infection with HIV occurred too recently, such as fewer than five days ago.
http://www.fda.gov/Cber/PMAlabel/P9500054LB.pdf
The AMPLICOR HIV-1 MONITOR Test is not intended to be used as a screening test for HIV or as a diagnostic test to confirm the presence of HIV infection.