Accuracy

Health Protection Agency evaluation¹ of 16 third-generation tests found that all except one had a sensitivity of 100% – in other words, all HIV-positive people tested were correctly diagnosed.

One test did fail to identify a single HIV-positive sample (of 533 tested). This sample was of the rare subtype O, and this test was judged to have a sensitivity of 99.8%.

The 16 tests all had a specificity of 99.8% or over – in other words, if 1000 HIV-negative people were tested, 998 would be correctly diagnosed as such, while two people’s samples would test positive. (However, in practice, all reactive [positive] results are checked with confirmatory tests, so individuals would not receive an incorrect diagnosis.)