Retrospective evaluation of western blot for detection of early HIV infections

The purpose of HIV diagnosis is to establish safely whether there is an infection or not. The enzyme-linked immunosorbent assay (ELISA) as screening test, and the western blot assay for confirmation is the most widely used serologic test system to get this information. Diagnostic problems occur if the two tests yield different results. In our 1993 study 491 (4.4%) of 11,127 tested sera were reactive by ELISA. 39 (7.9%) of these samples could not be confirmed by western blot, giving negative or indeterminate results. In addition, 370 ELISA-negative samples were tested by HIV-1 western blot to detect the infection in the early stage. 115 (31%) of these sera showed indeterminate western blot patterns, the other samples were negative. Results of follow-up investigations of 26 (Table 1) or 11 (Table 2) persons with indefinite serodiagnosis were analysed. HIV infection was not detected in any of these cases. In the literature, persons whose sera were reactive according to ELISA and were indeterminate in western blot, had a 3-5% probability of an aisting HIV infection. In contrast, indeterminate western blot patterns in ELISA-negative sere were without significance for the prognosis as to whether a person was or was not HIV-infected.