Diagnosis of HIV-infection

Two different blood tests are advised to confirm infection with HIV. In well equipped laboratories antibodies to HIV can be determined with an ELISA test. If the result is positive, a control is performed using a so called Western blot, though this is a very expensive test. The performance of a second (technically different) ELISA test or of a rapid test has been proposed for developing areas. A virus culture and PCR for HIV can be carried out if in doubt or for research purposes, though these are difficult techniques. Electricity is needed for ELISA tests, as well as the necessary apparatus and personnel who can use and maintain the equipment. If the tests are available and if priorities have to be set, the blood bank must be considered first (checking of blood donors). In the period before seroconversion, the serology is negative, even though there is infection. Viral proteins can be detected in the blood using antigen detection. The problem of this “window” in HIV detection (for example in blood donors) is especially significant in regions with high prevalence of HIV. These quite complicated tests may often not be available in rural areas. The “HIV check” test, which can be performed under quite primitive conditions, is easier to carry out than an ELISA. Current ELISA tests detect HIV-1 and HIV-2 simultaneously.

The diagnosis in children under 15 months is difficult with simple tests. All children born from seropositive mothers will be seropositive. Antibodies in the blood may originate from the mother or from the child itself. The maternal antibodies disappear spontaneously from the child’s blood in the course of the following months. After 18 months (usually earlier) they are no longer detectable. Children who are infected with HIV produce their own anti-HIV antibodies and will thus remain seropositive, despite the disappearance of the maternal antibodies. There are other techniques besides serology to determine whether or not a child is infected. Detection of a viral antigen (p24 antigen) in the child’s blood is a specific but rather insensitive test (only about 15% of infected children have a positive antigen test in their first year of life). Infection can be demonstrated by PCR (polymerase chain reaction) and virus culture, though these can also give false negative results in infected newborn babies.

Category: Medical Subject Notes , Medicine Notes