5. How is it diagnosed?
Once an infection has occurred, the virus multiplies inside the body for some time before the immune system responds and produces specific antibodies. (Antibodies are proteins produced by the immune system to fight an intruder.) The production of antibodies may not begin until weeks or even months after the infection. Once they are present, they can be detected by a blood test – the HIV antibody test. It provides indirect proof: If antibodies to the virus are present, then the virus itself must also be present. Finding the antibodies means that the test result is positive. The person is infected or, in everyday language, is “HIV positive”. If no antibodies are found, the test result is negative. The person is not infected and hence is called “HIV negative”. The tests are usually taken in a doctor’s office or a health clinic. An appointment is then made for learning the results which are usually available after one week. However, there are now also some “Rapid Tests” that show results within 10-30 minutes. One of these new rapid tests uses oral fluid instead of blood. Finally, there are also “Home Test Kits” that allow people to take their own small blood samples at home and send them to a laboratory which will then tell them the results.
Tests for HIV antibodies have to be repeated to be confirmed. The reason for this is the possibility of “false positive” and “false negative” results which must be excluded. There is also a chance that the test was taken “too early”, i.e. before the antibodies were formed. Thus, the test result could be negative in spite of an infection. Repeating the test a few weeks later may then show a positive result. The first test is called “ELISA”. For the confirmation of a positive result another test is used called “Western Blot”. An infection is confirmed only if both kinds of tests are positive.
Once an HIV infections has been established, other tests are used to monitor its progress and the state of the immune system.