All four of the selected HIV-1 specific primer sets detected group M, subtype B, the most common subtype of HIV-1 in the Americas and Western Europe [35] , at 50-00 genome copies/ml of plasma. However, the array was able to amplify all other subtypes, excluding subtype F, of HIV-1 group M with only one primer set (NP170/171), targeting the conserved pol region, at 100-1,000 genome copies/ml of plasma. In addition, the array amplified the group N isolate at 1,000 copies/ml with another primer set (NP175/174) targeting the conserved pol region. All the selected HIV-1 specific primer sets of the array failed to amplify the group O isolate (detection limit is .1,000 copies/ml of plasma). In comparison, the limit of detection (LOD) of recently improved commercial multiplex NAT assays for the broad spectrum of HIV-1 group M isolates is 40 copies/ml, and the LOD for group O is 200 copies/ml [36] [37] [38] . Thus, specific primer sets targeting group O isolates of HIV-1, as well as subtype F (group M) will need to be included in the array to increase the coverage of all existing subtypes/groups of the HIV-1. No crossreactivity was shown for HIV-1 or HIV-2 specific primers with the other type of HIV in a testing with medically relevant levels of viruses in a diversity panel containing 25 different HIV-1 isolates and three natural HIV-2 isolates collected worldwide.