[HIV diagnosis 1998]

Abstract

Due to considerable technical progress during the last few years the diagnosis of HIV-infection has been substantially improved. Third generation antibody screening assays, which also detect antibodies of the IgM and IgA type, have considerably narrowed the immunological window. The determination of the viral load in peripheral blood employing nucleic acid amplification techniques is now generally available and used for diagnostic and prognostic purposes as well as for the monitoring of antiviral therapy. To detect a HIV-infection the antibody screening assay is primarily used and complemented by the HIV-1 p24 antigen assay provided an early primary infection is suspected. In the latter case the antibody screening assay is often negative or indeterminate, while the p24 antigen assay is positive. According to the 1998 guidelines of the Federal Office for Public Health, the physician will be informed of the screening assay result without the need to await a confirmatory test in case of a reactive screening assay in the first sample. Confirmation, e.g. by immunoblot, will be done in a second blood sample which should be sent to the laboratory as soon as possible. EDTA-blood is recommended for this purpose, because it is best suited for quantification of plasma viremia, which has become a prerequisite for the institution and follow-up of antiretroviral treatment. The second sample will also serve to exclude false positive results due to clerical errors, and to determine the type of HIV, i.e. HIV-1 or HIV-2. The concept outlined should accelerate the availability of reactive test results to the physician and should reduce the cost of the diagnostic procedure.