What is the accuracy of the fda approved rna test for hiv at 18 days post pep?

Uncertain...: There has been little or no research on the extent to which PEP, if unsuccessful in preventing HIV, delays diagnostic test conversion. Probably a negative RNA test 18 days after completing PEP is close to 100% reliable, but nobody knows for sure. Some experts continue testing for 3-6 months after PEP. That's one of its disadvantages: prolongation of the period of uncertainty and anxiety.