Discrepant Results of 2 Screening Tests for Anti‐HIV Antibody

SIR—We are reporting an investigation of apparent discrepancies between the results of 2 different EIA screening tests for anti-HIV antibody. The discrepancy was brought to our attention by a review of test results obtained for a cohort of patients previously enrolled in a clinical trial of a candidate HIV vaccine. The trial was conducted from 1994 through 1995 to evaluate the antibody response to HIV core antigen p24 in HIV-seronegative subjects. This was one of numerous approaches that have been tested in HIV vaccine trials (for review, see [1]). After vaccination, participants at our institution had positive test results when a commercial HIV-antibody screening assay was used (HIVAB HIV-1/HIV-2 [rDNA] EIA; Abbott Laboratories [hereafter referred to as the “Abbott test”]), and the presence of anti-p24 antibody was confirmed by Western blotting (Cambridge Biotech HIV-1 Western Blot kit; Calyptebiomedical) (authors' unpublished data). A different commercial HIV-antibody EIA screening test (Genetic Systems HIV-1/HIV-2 Peptide EIA; Sanofi Diagnostics Pasteur [hereafter referred to as the “Sanofi test”]) started being used at our institution in early 2001. This was prompted by the federal requirement to use a method approved by the US Food and Drug Administration (FDA) for transplantation donor testing of cadaveric serum specimens [2]. To date, the Sanofi test is the only test approved for this application [3]. For practical reasons, our institution chose to use the Sanofi test for all HIV screening. Subsequently, 2 participants in the vaccine clinical trial were tested for HIV infection as part of routine medical care and were found to be seronegative when the Sanofi test was used. However, these participants tested positive when the Abbott test was used and continued to show reactivity to p24 antigen only when Western blotting was done. Subsequently, samples from a total of 8 participants in vaccine trials were retested by the Sanofi and the Abbott screening tests and by Western blotting. All showed p24 reactivity by Western blotting, all were seropositive by the Abbott test, and all were seronegative by the Sanofi test.