Sensitivity
Health Protection Agency evaluation1 of ten fourth-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 (Abbott Murex HIV Ag/Ab combination) did fail to identify a single HIV-positive sample (of 508 tested). This sample was of HIV-2, and this test was judged to have a sensitivity of 99.8%.
A WHO evaluation of five tests found that each had a sensitivity of 100%.2
A French evaluation of twelve tests found that nine had a sensitivity of 100%. Two tests did fail to identify a single HIV-positive sample (of 669 tested), and were judged to have a sensitivity of 99.8%. These tests were the Vidas Duo and Enzygnost HIV Integral. The samples missed were of subtypes F and C.3
Evaluation of the Abbott Architect Ag/Ab test, testing 3386 HIV-positive samples, found that it had a sensitivity of 99.94%.4 A smaller study of the use of the same test in sexually transmitted infection (STI) clinics found that it had a sensitivity of 100%.5
A study of the Bio-Rad GS HIV Combo Ag/Ab, testing 1340 HIV-positive samples, found that it had a sensitivity of 100%.6.
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Sensitivity and specificity
Specificity
The 10 tests evaluated by the HPA all had a specificity of 99.7% or over – in other words, if 1000 HIV-negative people were tested, 997 would be correctly diagnosed as such, while three people’s samples would be reactive (positive). (However, in practice, all reactive results are checked with confirmatory tests, so individuals would not receive an incorrect diagnosis.)
The WHO evaluation found that the specificity of the kits they assessed was somewhat variable:
Genscreen Plus HIV Ag/Ab – 98.3%
Vironostika HIV Uni-Form II Ag/Ab – 99.0%
Abbott Murex HIV Ag/Ab Combination – 99.3%
Genedia HIV Ag-Ab – 99.7%
Enzygnost HIV Integral II – 100%
The French evaluation of twelve fourth-generation kits noted a significant improvement in specificity when comparing the tests launched before and after 2000. The older tests had a specificity of between 99.4% and 99.6%; the newer tests ranged between 99.8% and 100%.3
Evaluation of the Abbott Architect Ag/Ab test, testing 7551 HIV-negative samples, found that it had a specificity of 98.78% (95% confidence interval 98.51-99.02%). The manufacturer recommends that all reactive (positive) samples are immediately re-tested with the same test in order to identify false-positives. Doing so increased specificity to 99.50% (95% confidence interval 99.31-99.64%).4
The smaller study of the test in STI clinics found that it had a specificity of 99.9%.5
A study of the Bio-Rad GS HIV Combo Ag/Ab, testing 6100 HIV-negative samples, found that it had a specificity of 99.89%.6