Reduction of the diagnostic window with a new combined p24 antigen and human immunodeficiency virus antibody screening assay.

In order to reduce the window phase between time of human immunodeficiency virus (HIV) infection and laboratory diagnosis, new fourth generation screening assays which permit a simultaneous detection of HIV antigen and antibody have been developed. In a multicenter study, a new automated fourth generation assay, Enzymun-Test HIV Combi (Boehringer Mannheim GmbH) was compared to third generation assay, p24 antigen tests and Western blot. A total of 37 seroconversion panels, samples of the early infection (n = 42), HIV-1 antibody positive sera, including subtypes A E, and O (n = 1118), HIV-2 positive samples (n = 252) and cell culture supernatants infected with different HIV-1 subtypes and HIV-2 (n = 50), blood donors (n = 6649), hospitalized patients (n = 475), HIV neg. sera with indeterminate Western blot (n = 32), potentially cross reactive serum samples (n = 435) and HIV negative specimens from Cameroon (n = 68) were tested. A total of 16 of 29 seroconversions were detected on average 8.5 days earlier with Enzymun-Test HIV Combi than HIV-1/HIV-2 3rd generation EIA (Abbott Laboratories). Overall, in the 29 panels investigated comparatively with the two assays, the mean time delay between Enzymun-Test HIV Combi and HIV-1/HIV-2 3rd generation EIA was 4.7 days. HIV antigen was detected in three out of 35 seroconversions one bleed earlier with HIV-1 Ag Monoclonal than with Enzymun-Test HIV Combi. Enzymun-Test HIV Combi showed a sensitivity of 100% for HIV antibody detection for HIV-1 group M and O and HIV-2 positive specimens. While p24 antigen of different HIV-1 subtypes was detected with Enzymun-Test HIV Combi in all the 49 cell culture supernatants, HIV Ag was not detected in an HIV-2 virus lysate. A total of 66 false positive results out of 7659 HIV negative samples were obtained with the Enzymun-Test HIV Combi. The specificity for unselected blood donors was 99.6%. The Enzymun-Test HIV Combi permits an earlier diagnosis of HIV infection than third generation assays through the detection of p24 antigen, which may be present in serum samples from individuals with recent HIV infection prior to seroconversion and it shows an excellent sensitivity for antibodies to all known HIV-1 subtypes and HIV-2. The specificity in blood donors and hospitalized patients is comparable to that of other assays.