ABSTRACT
Introduction: The screening methods for determination of HIV infection have been developedfrom the first-generation to the fourth-generation assays. The fourth-generation assays are thecombination methods that can detect HIV-1, HIV-2 antibodies and HIV p24 antigen. In this study, e evaluate two fourth-generation assays, AxSym HIV Ag/Ab Combo (Enzyme-linkedimmunosorbent assay; ELISA, Abbott laboratories) and Cobas HIV Ag/Ab Combi (Electrochemiluminescenceimmunoassay; ECLIA, Roche diagnostics).Methods: Serum specimens of 64 patients received from routine laboratory for HIV testing and26 plasma samples from donors of Khon Kaen Hospital were tested for HIV infection using twofourth-generation assays and three anti-HIV screening assays. These consist of a third generation antibody assay (AxSym HIV 1/2 gO; ELISA), a gelatin particle agglutination test (GPA) and immunochromatiographic test (ICT). The validity of the two fourth-generation assays were evaluated in relation to sensitivity, specificity, predictive value and likelihood.Results: The AxSym HIV Ag/Ab Combo demonstrated high sensitivity (100%, 95% CI:100-100%) and low specificity (97.50%, 95% CI:93-100%) with 96.55% (95% CI:90-100%) and 100% (95% CI:100-100%) of PPV and NPV, respectively. Similarly, Cobas HIV Ag/Ab Combi showed high sensitivity (100%, 95% CI:100-100%) and low specificity (96.07%, 95% CI:91-100%) with 94.11%(95% CI:86-100%) and 100% (95% CI:100-100%) of PPV and NPV, respectively. The positivelikelihood ratio of AxSym HIV Ag/Ab Combo was 40 (95% CI:5.77-277.06%) and Cobas HIVAg/Ab Combi was 25 (95% CI:6.55-99.20%).Conclusions: The two fourth-generation assays have high sensitivity and low specificity. Therefore, individual diagnosis of HIV infection using the fourth-generation assays should be performed under good laboratory practices.