What you should know about the test

What you should know about the test

The test used to ascertain whether someone has become infected with the AIDS Virus, HIV, is called the HIV antibody test (e.g. the ELISA). What is looked for is not the virus itself, but the products of the human defence system (immune system) in the blood, i.e. the antibodies.

The HIV test is one of the surest tests in medicine.
The time from the moment of infection until the appearance of antibodies in the blood (seroconversion time, diagnostic window) varies, and is dependent on various factors (route of transmission, number of virus particles transmitted, etc.). As far as we know today, antibodies appear at the earliest after two to six weeks and, in the majority of people within three months, and therefore testing is effective at the earliest two to six weeks after exposure to risk of infection. If the result is then negative, the test should be repeated 3 months later.

There are various tests, and these complement each other. The ELISA is used as an HIV antibody detection test. Since other antibodies may also interact, "positive" results are always rechecked. For confirmation or correction the Western Blot Test is used. It is more time-consuming and expensive than the more sensitive ELISA. To exclude possible sample switches in the laboratory, in the event of a "positive" result a second blood sample is to be recommended.

Antigen tests, which demonstrate viral components directly, are less sensitive than the HIV antibody test, and give no essential shortening of the diagnostic window. The antigen test is important in identifying those newly infected with HIV. The PCR test (gene probes, with which even traces of genetic material of the virus can be detected) is, because of its complexity, used only by specialists and when test results are unclear e.g. in early diagnosis in infants and uncertain cases of infection with HIV. The PCR Test is nowadays used to measure the effectiveness of therapy.