The diagnosis of HIV infection is determined differently in mothers and babies.
Mothers are said to be HIV infected if a blood sample is shown to contain antibodies. Antibodies are proteins produced by the immune system in response to microbes including bacteria and viruses and they combine chemically with the virus or parts of the microbe. In practice the antibodies are demonstrated by mixing serum from a mother in a test tube with some proteins said to come from HIV. It there are antibodies they announce their presence by causing a colour change in the solution as they react with the virus proteins. If there are no antibodies nothing happens. There is no colour change. So to do an antibody test, first you need to obtain the proteins unique to HIV.
The identity of proteins used in HIV antibody tests is based on research published in 1983 by Montagnier and in 1984 by Gallo. Both scientists claimed to have isolated and purified HIV from cell cultures of tissues of AIDS patients. Itís important to note that this research is the whole basis of the existence of HIV, HIV proteins, the antibody tests and the HIV theory of AIDS.