A type of nucleic acid testing done after a reactive multiplex NAT. Multiplex NAT (mNAT) tests multiple donors whose samples have been pooled into one testing sample for three different organisms: HIV-1, hepatitis C virus (HCV), and hepatitis B virus (HBV). If the test is negative, all of the donors in the pool are considered negative for all three viruses. If the mNAT is positive, however, the testing laboratory must determine which donor is positive for which virus. The discriminatory NAT tests for only ONE of the three viruses mentioned above, and it is a tool for the lab to identify the positive donor (or donors) from the original pool of donors tested.