[Sensitivity and specificity of test results in HIV]

In HIV tests, the sensitivity is important, but even more so is the specificity, i.e., the reliability of positive tests results. A third parameter, the positive predictive value, is connected with these test characteristics; but even more it depends to a high degree on the prevalence of the infection. To solve these general problems, highly purified virus antigens as well as step testing are used in HIV diagnosis. Initially, screenings test (ELISA, IFA, various so-called quick tests) are used to filter out those suspected of being infected from the mass of non-infected persons. For this population with an increased HIV prevalence, confirmation tests are performed. With the indirect immunofluorescence assay, it is possible to distinguish antiviral from anticellular antibody reactions. With the so-called immunoblot, the immune response against individual virus proteins can be determined. The sensitivity of HIV tests is approximately 99-100%. As for the specificity, only 1 false positive result per 50,000-100,000 tests is expected. AIDS infections before seroconversion can be diagnosed only by detecting the virus or compounds of it. This is hardly possible with virus Antigen-ELISA and virus cultivation. On principle, nucleic acid hybridisation after DNA multiplication by polymerase chain reaction would be suitable. However, there are still some technical problems and questions of interpretation of results with this method. It is also very complicated and thus out of the question for routine examination.