GACPAT HIV 1+2: A simple, inexpensive assay to screen for, and discriminate between, anti‐HIV 1 and anti‐HIV 2

A simple and cheap assay suitable for screening for anti‐HIV 1 and anti‐HIV 2 and discriminating between them was evaluated. In it specimens are incubated in U‐bottomed microplate wells coated with anti‐human IgG for 30 min at room temperature. After washing, 100 μl of a 1 in 50 dilution of HIV 1‐coated gelatin particles (Serodia‐HIV 1/2, Fujirebio) are added. Settling patterns are read on the second day: A positive reaction is indicated by adherence of the particles and a negative by a button. The HIV 1 particles are then washed away and HIV 2 particles added. Anti‐HIV 2 reaction patterns are read on the third day. To assess the performance of the modified “GACPAT HIV 1+2” assay a panel of 1,621 serum/plasma specimens was used. It comprised validated anti‐HIV 1 positive (n = 220), anti‐HIV 2 positive (n = 214), dual anti‐HIV 1/anti‐HIV 2 positive (n = 11), and anti‐HIV negative (n = 1,176) serum/plasma specimens. All 434 specimens that contained anti‐HIV 1 or anti‐HIV 2 reacted positively with the homologous particles. The 11 dually positive specimens reacted positively with both HIV 1 and HIV 2 particles. Five (2.3%) anti‐HIV 1 and five (2.3%) anti‐HIV 2 positive specimens gave positive reactions with both particle types, but none of the five cross‐reactive anti‐HIV 2 specimens were dually reactive when the order of particle addition was reversed. One repeat false positive reaction was recorded with the HIV 1 particles and none with the HIV 2 particles, giving specificities of 99.9% and 100%, respectively. Type specificity was 98.8% after the results of the reverse assay had been taken into account. The assay was sensitive for anti‐HIV 1 in seroconversion series and for anti‐HIV 2 in highly diluted specimens. GACPAT HIV 1 +2 is an accurate anti‐HIV assay applicable to serum/plasma. With few exceptions anti‐HIV 1 positive specimens are reactive only on the second day and anti‐HIV 2 positive specimens only on the third day. It thus discriminates anti‐HIV 2 from anti‐HIV 1, probably through depletion of cross‐reacting antibodies by the reaction with the particles initially added. © 1995 Wiley‐Liss, Inc.